diff --git a/dist/xstream.js b/dist/xstream.js
index c0c010f..e54ca86 100644
--- a/dist/xstream.js
+++ b/dist/xstream.js
@@ -34,6 +34,11 @@ function invoke(f, args) {
         default: return f.apply(void 0, args);
     }
 }
+function compose2(f1, f2) {
+    return function composedFn(arg) {
+        return f1(f2(arg));
+    };
+}
 var CombineListener = (function () {
     function CombineListener(i, prod) {
         this.i = i;
@@ -1007,6 +1012,14 @@ var Stream = (function () {
             var prod = this._prod;
             return new Stream(new FilterMapOperator(prod.predicate, project, prod.ins));
         }
+        if (this._prod instanceof FilterMapOperator) {
+            var prod = this._prod;
+            return new Stream(new FilterMapOperator(prod.predicate, compose2(project, prod.project), prod.ins));
+        }
+        if (this._prod instanceof MapOperator) {
+            var prod = this._prod;
+            return new Stream(new MapOperator(compose2(project, prod.project), prod.ins));
+        }
         return new Stream(new MapOperator(project, this));
     };
     /**
@@ -1028,6 +1041,18 @@ var Stream = (function () {
         return new Stream(new MapToOperator(projectedValue, this));
     };
     Stream.prototype.filter = function (predicate) {
+        if (this._prod instanceof MapOperator) {
+            var prod = this._prod;
+            return new Stream(new FilterMapOperator(predicate, prod.project, prod.ins));
+        }
+        if (this._prod instanceof FilterMapOperator) {
+            var prod = this._prod;
+            return new Stream(new FilterMapOperator(compose2(predicate, prod.predicate), prod.project, prod.ins));
+        }
+        if (this._prod instanceof FilterOperator) {
+            var prod = this._prod;
+            return new Stream(new FilterOperator(compose2(predicate, prod.predicate), prod.ins));
+        }
         return new Stream(new FilterOperator(predicate, this));
     };
     Stream.prototype.take = function (amount) {
diff --git a/dist/xstream.min.js b/dist/xstream.min.js
index 46f87d0..1e9192b 100644
--- a/dist/xstream.min.js
+++ b/dist/xstream.min.js
@@ -1 +1 @@
-(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.xstream=f()}})(function(){var define,module,exports;return function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s}({1:[function(require,module,exports){"use strict";var __extends=this&&this.__extends||function(d,b){for(var p in b)if(b.hasOwnProperty(p))d[p]=b[p];function __(){this.constructor=d}d.prototype=b===null?Object.create(b):(__.prototype=b.prototype,new __)};var empty={};function noop(){}var emptyListener={_n:noop,_e:noop,_c:noop};function internalizeProducer(producer){producer._start=function _start(il){il.next=il._n;il.error=il._e;il.complete=il._c;this.start(il)};producer._stop=producer.stop}function invoke(f,args){switch(args.length){case 0:return f();case 1:return f(args[0]);case 2:return f(args[0],args[1]);case 3:return f(args[0],args[1],args[2]);case 4:return f(args[0],args[1],args[2],args[3]);case 5:return f(args[0],args[1],args[2],args[3],args[4]);default:return f.apply(void 0,args)}}var CombineListener=function(){function CombineListener(i,prod){this.i=i;this.prod=prod;prod.proxies.push(this)}CombineListener.prototype._n=function(t){var prod=this.prod;var vals=prod.vals;prod.hasVal[this.i]=true;vals[this.i]=t;if(!prod.ready){prod.up()}if(prod.ready){try{prod.out._n(invoke(prod.project,vals))}catch(e){prod.out._e(e)}}};CombineListener.prototype._e=function(err){this.prod.out._e(err)};CombineListener.prototype._c=function(){var prod=this.prod;if(--prod.ac===0){prod.out._c()}};return CombineListener}();var CombineProducer=function(){function CombineProducer(project,streams){this.project=project;this.streams=streams;this.out=emptyListener;this.proxies=[];this.ready=false;this.vals=new Array(streams.length);this.hasVal=new Array(streams.length);this.ac=streams.length}CombineProducer.prototype.up=function(){for(var i=this.hasVal.length-1;i>=0;i--){if(!this.hasVal[i]){return}}this.ready=true};CombineProducer.prototype._start=function(out){this.out=out;var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._add(new CombineListener(i,this))}};CombineProducer.prototype._stop=function(){var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._remove(this.proxies[i])}this.out=null;this.ac=streams.length;this.proxies=[];this.ready=false;this.vals=new Array(streams.length);this.hasVal=new Array(streams.length)};return CombineProducer}();var FromArrayProducer=function(){function FromArrayProducer(a){this.a=a}FromArrayProducer.prototype._start=function(out){var a=this.a;for(var i=0,l=a.length;i<l;i++){out._n(a[i])}out._c()};FromArrayProducer.prototype._stop=function(){};return FromArrayProducer}();var FromPromiseProducer=function(){function FromPromiseProducer(p){this.p=p;this.on=false}FromPromiseProducer.prototype._start=function(out){var prod=this;this.on=true;this.p.then(function(v){if(prod.on){out._n(v);out._c()}},function(e){out._e(e)}).then(null,function(err){setTimeout(function(){throw err})})};FromPromiseProducer.prototype._stop=function(){this.on=false};return FromPromiseProducer}();var MergeProducer=function(){function MergeProducer(streams){this.streams=streams;this.out=emptyListener;this.ac=streams.length}MergeProducer.prototype._start=function(out){this.out=out;var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._add(this)}};MergeProducer.prototype._stop=function(){var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._remove(this)}this.out=null;this.ac=streams.length};MergeProducer.prototype._n=function(t){this.out._n(t)};MergeProducer.prototype._e=function(err){this.out._e(err)};MergeProducer.prototype._c=function(){if(--this.ac===0){this.out._c()}};return MergeProducer}();var PeriodicProducer=function(){function PeriodicProducer(period){this.period=period;this.intervalID=-1;this.i=0}PeriodicProducer.prototype._start=function(stream){var self=this;function intervalHandler(){stream._n(self.i++)}this.intervalID=setInterval(intervalHandler,this.period)};PeriodicProducer.prototype._stop=function(){if(this.intervalID!==-1)clearInterval(this.intervalID);this.intervalID=-1;this.i=0};return PeriodicProducer}();var DebugOperator=function(){function DebugOperator(spy,ins){if(spy===void 0){spy=null}this.spy=spy;this.ins=ins;this.out=null}DebugOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};DebugOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};DebugOperator.prototype._n=function(t){if(this.spy){try{this.spy(t)}catch(e){this.out._e(e)}}else{console.log(t)}this.out._n(t)};DebugOperator.prototype._e=function(err){this.out._e(err)};DebugOperator.prototype._c=function(){this.out._c()};return DebugOperator}();var DropOperator=function(){function DropOperator(max,ins){this.max=max;this.ins=ins;this.out=null;this.dropped=0}DropOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};DropOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.dropped=0};DropOperator.prototype._n=function(t){if(this.dropped++>=this.max)this.out._n(t)};DropOperator.prototype._e=function(err){this.out._e(err)};DropOperator.prototype._c=function(){this.out._c()};return DropOperator}();var OtherListener=function(){function OtherListener(out,op){this.out=out;this.op=op}OtherListener.prototype._n=function(t){this.op.end()};OtherListener.prototype._e=function(err){this.out._e(err)};OtherListener.prototype._c=function(){this.op.end()};return OtherListener}();var EndWhenOperator=function(){function EndWhenOperator(o,ins){this.o=o;this.ins=ins;this.out=null;this.oli=emptyListener}EndWhenOperator.prototype._start=function(out){this.out=out;this.o._add(this.oli=new OtherListener(out,this));this.ins._add(this)};EndWhenOperator.prototype._stop=function(){this.ins._remove(this);this.o._remove(this.oli);this.out=null;this.oli=null};EndWhenOperator.prototype.end=function(){this.out._c()};EndWhenOperator.prototype._n=function(t){this.out._n(t)};EndWhenOperator.prototype._e=function(err){this.out._e(err)};EndWhenOperator.prototype._c=function(){this.end()};return EndWhenOperator}();var FilterOperator=function(){function FilterOperator(predicate,ins){this.predicate=predicate;this.ins=ins;this.out=null}FilterOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FilterOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};FilterOperator.prototype._n=function(t){try{if(this.predicate(t))this.out._n(t)}catch(e){this.out._e(e)}};FilterOperator.prototype._e=function(err){this.out._e(err)};FilterOperator.prototype._c=function(){this.out._c()};return FilterOperator}();var FCInner=function(){function FCInner(out,op){this.out=out;this.op=op}FCInner.prototype._n=function(t){this.out._n(t)};FCInner.prototype._e=function(err){this.out._e(err)};FCInner.prototype._c=function(){this.op.less()};return FCInner}();var FlattenConcOperator=function(){function FlattenConcOperator(ins){this.ins=ins;this.active=1;this.out=null}FlattenConcOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FlattenConcOperator.prototype._stop=function(){this.ins._remove(this);this.active=1;this.out=null};FlattenConcOperator.prototype.less=function(){if(--this.active===0){this.out._c()}};FlattenConcOperator.prototype._n=function(s){this.active++;s._add(new FCInner(this.out,this))};FlattenConcOperator.prototype._e=function(err){this.out._e(err)};FlattenConcOperator.prototype._c=function(){this.less()};return FlattenConcOperator}();exports.FlattenConcOperator=FlattenConcOperator;var FInner=function(){function FInner(out,op){this.out=out;this.op=op}FInner.prototype._n=function(t){this.out._n(t)};FInner.prototype._e=function(err){this.out._e(err)};FInner.prototype._c=function(){this.op.curr=null;this.op.less()};return FInner}();var FlattenOperator=function(){function FlattenOperator(ins){this.ins=ins;this.curr=null;this.inner=null;this.open=true;this.out=null}FlattenOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FlattenOperator.prototype._stop=function(){this.ins._remove(this);this.curr=null;this.inner=null;this.open=true;this.out=null};FlattenOperator.prototype.cut=function(){var _a=this,curr=_a.curr,inner=_a.inner;if(curr&&inner){curr._remove(inner)}};FlattenOperator.prototype.less=function(){if(!this.open&&!this.curr){this.out._c()}};FlattenOperator.prototype._n=function(s){this.cut();(this.curr=s)._add(this.inner=new FInner(this.out,this))};FlattenOperator.prototype._e=function(err){this.out._e(err)};FlattenOperator.prototype._c=function(){this.open=false;this.less()};return FlattenOperator}();exports.FlattenOperator=FlattenOperator;var FoldOperator=function(){function FoldOperator(f,seed,ins){this.f=f;this.seed=seed;this.ins=ins;this.out=null;this.acc=seed}FoldOperator.prototype._start=function(out){this.out=out;out._n(this.acc);this.ins._add(this)};FoldOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.acc=this.seed};FoldOperator.prototype._n=function(t){try{this.out._n(this.acc=this.f(this.acc,t))}catch(e){this.out._e(e)}};FoldOperator.prototype._e=function(err){this.out._e(err)};FoldOperator.prototype._c=function(){this.out._c()};return FoldOperator}();var LastOperator=function(){function LastOperator(ins){this.ins=ins;this.out=null;this.has=false;this.val=empty}LastOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};LastOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.has=false;this.val=empty};LastOperator.prototype._n=function(t){this.has=true;this.val=t};LastOperator.prototype._e=function(err){this.out._e(err)};LastOperator.prototype._c=function(){var out=this.out;if(this.has){out._n(this.val);out._c()}else{out._e("TODO show proper error")}};return LastOperator}();var MFCInner=function(){function MFCInner(out,op){this.out=out;this.op=op}MFCInner.prototype._n=function(t){this.out._n(t)};MFCInner.prototype._e=function(err){this.out._e(err)};MFCInner.prototype._c=function(){this.op.less()};return MFCInner}();var MapFlattenConcOperator=function(){function MapFlattenConcOperator(mapOp){this.mapOp=mapOp;this.active=1;this.out=null}MapFlattenConcOperator.prototype._start=function(out){this.out=out;this.mapOp.ins._add(this)};MapFlattenConcOperator.prototype._stop=function(){this.mapOp.ins._remove(this);this.active=1;this.out=null};MapFlattenConcOperator.prototype.less=function(){if(--this.active===0){this.out._c()}};MapFlattenConcOperator.prototype._n=function(v){this.active++;try{this.mapOp.project(v)._add(new MFCInner(this.out,this))}catch(e){this.out._e(e)}};MapFlattenConcOperator.prototype._e=function(err){this.out._e(err)};MapFlattenConcOperator.prototype._c=function(){this.less()};return MapFlattenConcOperator}();var MFInner=function(){function MFInner(out,op){this.out=out;this.op=op}MFInner.prototype._n=function(t){this.out._n(t)};MFInner.prototype._e=function(err){this.out._e(err)};MFInner.prototype._c=function(){this.op.curr=null;this.op.less()};return MFInner}();var MapFlattenOperator=function(){function MapFlattenOperator(mapOp){this.mapOp=mapOp;this.curr=null;this.inner=null;this.open=true;this.out=null}MapFlattenOperator.prototype._start=function(out){this.out=out;this.mapOp.ins._add(this)};MapFlattenOperator.prototype._stop=function(){this.mapOp.ins._remove(this);this.curr=null;this.inner=null;this.open=true;this.out=null};MapFlattenOperator.prototype.cut=function(){var _a=this,curr=_a.curr,inner=_a.inner;if(curr&&inner){curr._remove(inner)}};MapFlattenOperator.prototype.less=function(){if(!this.open&&!this.curr){this.out._c()}};MapFlattenOperator.prototype._n=function(v){this.cut();try{(this.curr=this.mapOp.project(v))._add(this.inner=new MFInner(this.out,this))}catch(e){this.out._e(e)}};MapFlattenOperator.prototype._e=function(err){this.out._e(err)};MapFlattenOperator.prototype._c=function(){this.open=false;this.less()};return MapFlattenOperator}();var MapOperator=function(){function MapOperator(project,ins){this.project=project;this.ins=ins;this.out=null}MapOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};MapOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};MapOperator.prototype._n=function(t){try{this.out._n(this.project(t))}catch(e){this.out._e(e)}};MapOperator.prototype._e=function(err){this.out._e(err)};MapOperator.prototype._c=function(){this.out._c()};return MapOperator}();var FilterMapOperator=function(){function FilterMapOperator(predicate,project,ins){this.predicate=predicate;this.project=project;this.ins=ins;this.out=null}FilterMapOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FilterMapOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};FilterMapOperator.prototype._tryCatch=function(v){try{this.out._n(this.project(v))}catch(e){this.out._e(e)}};FilterMapOperator.prototype._n=function(v){if(this.predicate(v)){this._tryCatch(v)}};FilterMapOperator.prototype._e=function(e){this.out._e(e)};FilterMapOperator.prototype._c=function(){this.out._c()};return FilterMapOperator}();var MapToOperator=function(){function MapToOperator(val,ins){this.val=val;this.ins=ins;this.out=null}MapToOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};MapToOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};MapToOperator.prototype._n=function(t){this.out._n(this.val)};MapToOperator.prototype._e=function(err){this.out._e(err)};MapToOperator.prototype._c=function(){this.out._c()};return MapToOperator}();var ReplaceErrorOperator=function(){function ReplaceErrorOperator(fn,ins){this.fn=fn;this.ins=ins;this.out=empty}ReplaceErrorOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};ReplaceErrorOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};ReplaceErrorOperator.prototype._n=function(t){this.out._n(t)};ReplaceErrorOperator.prototype._e=function(err){try{this.ins._remove(this);(this.ins=this.fn(err))._add(this)}catch(e){this.out._e(e)}};ReplaceErrorOperator.prototype._c=function(){this.out._c()};return ReplaceErrorOperator}();var StartWithOperator=function(){function StartWithOperator(ins,value){this.ins=ins;this.value=value;this.out=emptyListener}StartWithOperator.prototype._start=function(out){this.out=out;this.out._n(this.value);this.ins._add(out)};StartWithOperator.prototype._stop=function(){this.ins._remove(this.out);this.out=null};return StartWithOperator}();var TakeOperator=function(){function TakeOperator(max,ins){this.max=max;this.ins=ins;this.out=null;this.taken=0}TakeOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};TakeOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.taken=0};TakeOperator.prototype._n=function(t){var out=this.out;if(this.taken++<this.max-1){out._n(t)}else{out._n(t);out._c();this._stop()}};TakeOperator.prototype._e=function(err){this.out._e(err)};TakeOperator.prototype._c=function(){this.out._c()};return TakeOperator}();var Stream=function(){function Stream(producer){this._stopID=empty;this.combine=function combine(project){var streams=[];for(var _i=1;_i<arguments.length;_i++){streams[_i-1]=arguments[_i]}streams.unshift(this);return Stream.combine.apply(Stream,[project].concat(streams))};this._prod=producer;this._ils=[]}Stream.prototype._n=function(t){var len=this._ils.length;if(len===1){this._ils[0]._n(t)}else{for(var i=0;i<len;i++){this._ils[i]._n(t)}}};Stream.prototype._e=function(err){var len=this._ils.length;if(len===1){this._ils[0]._e(err)}else{for(var i=0;i<len;i++){this._ils[i]._e(err)}}this._x()};Stream.prototype._c=function(){var len=this._ils.length;if(len===1){this._ils[0]._c()}else{for(var i=0;i<len;i++){this._ils[i]._c()}}this._x()};Stream.prototype._x=function(){if(this._ils.length===0)return;if(this._prod)this._prod._stop();this._ils=[]};Stream.prototype.addListener=function(listener){listener._n=listener.next;listener._e=listener.error;listener._c=listener.complete;this._add(listener)};Stream.prototype.removeListener=function(listener){this._remove(listener)};Stream.prototype._add=function(il){this._ils.push(il);if(this._ils.length===1){if(this._stopID!==empty){clearTimeout(this._stopID);this._stopID=empty}if(this._prod)this._prod._start(this)}};Stream.prototype._remove=function(il){var _this=this;var i=this._ils.indexOf(il);if(i>-1){this._ils.splice(i,1);if(this._prod&&this._ils.length<=0){this._stopID=setTimeout(function(){return _this._prod._stop()})}}};Stream.create=function(producer){if(producer){internalizeProducer(producer)}return new Stream(producer)};Stream.createWithMemory=function(producer){if(producer){internalizeProducer(producer)}return new MemoryStream(producer)};Stream.never=function(){return new Stream({_start:noop,_stop:noop})};Stream.empty=function(){return new Stream({_start:function(il){il._c()},_stop:noop})};Stream.throw=function(err){return new Stream({_start:function(il){il._e(err)},_stop:noop})};Stream.of=function(){var items=[];for(var _i=0;_i<arguments.length;_i++){items[_i-0]=arguments[_i]}return Stream.fromArray(items)};Stream.fromArray=function(array){return new Stream(new FromArrayProducer(array))};Stream.fromPromise=function(promise){return new Stream(new FromPromiseProducer(promise))};Stream.periodic=function(period){return new Stream(new PeriodicProducer(period))};Stream.merge=function(){var streams=[];for(var _i=0;_i<arguments.length;_i++){streams[_i-0]=arguments[_i]}return new Stream(new MergeProducer(streams))};Stream.prototype.map=function(project){if(this._prod instanceof FilterOperator){var prod=this._prod;return new Stream(new FilterMapOperator(prod.predicate,project,prod.ins))}return new Stream(new MapOperator(project,this))};Stream.prototype.mapTo=function(projectedValue){return new Stream(new MapToOperator(projectedValue,this))};Stream.prototype.filter=function(predicate){return new Stream(new FilterOperator(predicate,this))};Stream.prototype.take=function(amount){return new Stream(new TakeOperator(amount,this))};Stream.prototype.drop=function(amount){return new Stream(new DropOperator(amount,this))};Stream.prototype.last=function(){return new Stream(new LastOperator(this))};Stream.prototype.startWith=function(x){return new Stream(new StartWithOperator(this,x))};Stream.prototype.endWhen=function(other){return new Stream(new EndWhenOperator(other,this))};Stream.prototype.fold=function(accumulate,init){return new Stream(new FoldOperator(accumulate,init,this))};Stream.prototype.replaceError=function(replace){return new Stream(new ReplaceErrorOperator(replace,this))};Stream.prototype.flatten=function(){return new Stream(this._prod instanceof MapOperator?new MapFlattenOperator(this._prod):new FlattenOperator(this))};Stream.prototype.flattenConcurrently=function(){return new Stream(this._prod instanceof MapOperator?new MapFlattenConcOperator(this._prod):new FlattenConcOperator(this))};Stream.prototype.merge=function(other){return Stream.merge(this,other)};Stream.prototype.compose=function(operator){return operator(this)};Stream.prototype.remember=function(){return new MemoryStream(this._prod)};Stream.prototype.imitate=function(other){other._add(this)};Stream.prototype.debug=function(spy){if(spy===void 0){spy=null}return new Stream(new DebugOperator(spy,this))};Stream.prototype.shamefullySendNext=function(value){this._n(value)};Stream.prototype.shamefullySendError=function(error){this._e(error)};Stream.prototype.shamefullySendComplete=function(){this._c()};Stream.combine=function combine(project){var streams=[];for(var _i=1;_i<arguments.length;_i++){streams[_i-1]=arguments[_i]}return new Stream(new CombineProducer(project,streams))};return Stream}();exports.Stream=Stream;var MemoryStream=function(_super){__extends(MemoryStream,_super);function MemoryStream(producer){_super.call(this,producer);this._has=false}MemoryStream.prototype._n=function(x){this._val=x;this._has=true;_super.prototype._n.call(this,x)};MemoryStream.prototype._add=function(listener){if(this._has){listener._n(this._val)}_super.prototype._add.call(this,listener)};return MemoryStream}(Stream);exports.MemoryStream=MemoryStream;Object.defineProperty(exports,"__esModule",{value:true});exports.default=Stream},{}],2:[function(require,module,exports){"use strict";var core_1=require("./core");exports.Stream=core_1.Stream;exports.MemoryStream=core_1.MemoryStream;Object.defineProperty(exports,"__esModule",{value:true});exports.default=core_1.Stream},{"./core":1}]},{},[2])(2)});
\ No newline at end of file
+(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.xstream=f()}})(function(){var define,module,exports;return function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s}({1:[function(require,module,exports){"use strict";var __extends=this&&this.__extends||function(d,b){for(var p in b)if(b.hasOwnProperty(p))d[p]=b[p];function __(){this.constructor=d}d.prototype=b===null?Object.create(b):(__.prototype=b.prototype,new __)};var empty={};function noop(){}var emptyListener={_n:noop,_e:noop,_c:noop};function internalizeProducer(producer){producer._start=function _start(il){il.next=il._n;il.error=il._e;il.complete=il._c;this.start(il)};producer._stop=producer.stop}function invoke(f,args){switch(args.length){case 0:return f();case 1:return f(args[0]);case 2:return f(args[0],args[1]);case 3:return f(args[0],args[1],args[2]);case 4:return f(args[0],args[1],args[2],args[3]);case 5:return f(args[0],args[1],args[2],args[3],args[4]);default:return f.apply(void 0,args)}}function compose2(f1,f2){return function composedFn(arg){return f1(f2(arg))}}var CombineListener=function(){function CombineListener(i,prod){this.i=i;this.prod=prod;prod.proxies.push(this)}CombineListener.prototype._n=function(t){var prod=this.prod;var vals=prod.vals;prod.hasVal[this.i]=true;vals[this.i]=t;if(!prod.ready){prod.up()}if(prod.ready){try{prod.out._n(invoke(prod.project,vals))}catch(e){prod.out._e(e)}}};CombineListener.prototype._e=function(err){this.prod.out._e(err)};CombineListener.prototype._c=function(){var prod=this.prod;if(--prod.ac===0){prod.out._c()}};return CombineListener}();var CombineProducer=function(){function CombineProducer(project,streams){this.project=project;this.streams=streams;this.out=emptyListener;this.proxies=[];this.ready=false;this.vals=new Array(streams.length);this.hasVal=new Array(streams.length);this.ac=streams.length}CombineProducer.prototype.up=function(){for(var i=this.hasVal.length-1;i>=0;i--){if(!this.hasVal[i]){return}}this.ready=true};CombineProducer.prototype._start=function(out){this.out=out;var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._add(new CombineListener(i,this))}};CombineProducer.prototype._stop=function(){var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._remove(this.proxies[i])}this.out=null;this.ac=streams.length;this.proxies=[];this.ready=false;this.vals=new Array(streams.length);this.hasVal=new Array(streams.length)};return CombineProducer}();var FromArrayProducer=function(){function FromArrayProducer(a){this.a=a}FromArrayProducer.prototype._start=function(out){var a=this.a;for(var i=0,l=a.length;i<l;i++){out._n(a[i])}out._c()};FromArrayProducer.prototype._stop=function(){};return FromArrayProducer}();var FromPromiseProducer=function(){function FromPromiseProducer(p){this.p=p;this.on=false}FromPromiseProducer.prototype._start=function(out){var prod=this;this.on=true;this.p.then(function(v){if(prod.on){out._n(v);out._c()}},function(e){out._e(e)}).then(null,function(err){setTimeout(function(){throw err})})};FromPromiseProducer.prototype._stop=function(){this.on=false};return FromPromiseProducer}();var MergeProducer=function(){function MergeProducer(streams){this.streams=streams;this.out=emptyListener;this.ac=streams.length}MergeProducer.prototype._start=function(out){this.out=out;var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._add(this)}};MergeProducer.prototype._stop=function(){var streams=this.streams;for(var i=streams.length-1;i>=0;i--){streams[i]._remove(this)}this.out=null;this.ac=streams.length};MergeProducer.prototype._n=function(t){this.out._n(t)};MergeProducer.prototype._e=function(err){this.out._e(err)};MergeProducer.prototype._c=function(){if(--this.ac===0){this.out._c()}};return MergeProducer}();var PeriodicProducer=function(){function PeriodicProducer(period){this.period=period;this.intervalID=-1;this.i=0}PeriodicProducer.prototype._start=function(stream){var self=this;function intervalHandler(){stream._n(self.i++)}this.intervalID=setInterval(intervalHandler,this.period)};PeriodicProducer.prototype._stop=function(){if(this.intervalID!==-1)clearInterval(this.intervalID);this.intervalID=-1;this.i=0};return PeriodicProducer}();var DebugOperator=function(){function DebugOperator(spy,ins){if(spy===void 0){spy=null}this.spy=spy;this.ins=ins;this.out=null}DebugOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};DebugOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};DebugOperator.prototype._n=function(t){if(this.spy){try{this.spy(t)}catch(e){this.out._e(e)}}else{console.log(t)}this.out._n(t)};DebugOperator.prototype._e=function(err){this.out._e(err)};DebugOperator.prototype._c=function(){this.out._c()};return DebugOperator}();var DropOperator=function(){function DropOperator(max,ins){this.max=max;this.ins=ins;this.out=null;this.dropped=0}DropOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};DropOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.dropped=0};DropOperator.prototype._n=function(t){if(this.dropped++>=this.max)this.out._n(t)};DropOperator.prototype._e=function(err){this.out._e(err)};DropOperator.prototype._c=function(){this.out._c()};return DropOperator}();var OtherListener=function(){function OtherListener(out,op){this.out=out;this.op=op}OtherListener.prototype._n=function(t){this.op.end()};OtherListener.prototype._e=function(err){this.out._e(err)};OtherListener.prototype._c=function(){this.op.end()};return OtherListener}();var EndWhenOperator=function(){function EndWhenOperator(o,ins){this.o=o;this.ins=ins;this.out=null;this.oli=emptyListener}EndWhenOperator.prototype._start=function(out){this.out=out;this.o._add(this.oli=new OtherListener(out,this));this.ins._add(this)};EndWhenOperator.prototype._stop=function(){this.ins._remove(this);this.o._remove(this.oli);this.out=null;this.oli=null};EndWhenOperator.prototype.end=function(){this.out._c()};EndWhenOperator.prototype._n=function(t){this.out._n(t)};EndWhenOperator.prototype._e=function(err){this.out._e(err)};EndWhenOperator.prototype._c=function(){this.end()};return EndWhenOperator}();var FilterOperator=function(){function FilterOperator(predicate,ins){this.predicate=predicate;this.ins=ins;this.out=null}FilterOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FilterOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};FilterOperator.prototype._n=function(t){try{if(this.predicate(t))this.out._n(t)}catch(e){this.out._e(e)}};FilterOperator.prototype._e=function(err){this.out._e(err)};FilterOperator.prototype._c=function(){this.out._c()};return FilterOperator}();var FCInner=function(){function FCInner(out,op){this.out=out;this.op=op}FCInner.prototype._n=function(t){this.out._n(t)};FCInner.prototype._e=function(err){this.out._e(err)};FCInner.prototype._c=function(){this.op.less()};return FCInner}();var FlattenConcOperator=function(){function FlattenConcOperator(ins){this.ins=ins;this.active=1;this.out=null}FlattenConcOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FlattenConcOperator.prototype._stop=function(){this.ins._remove(this);this.active=1;this.out=null};FlattenConcOperator.prototype.less=function(){if(--this.active===0){this.out._c()}};FlattenConcOperator.prototype._n=function(s){this.active++;s._add(new FCInner(this.out,this))};FlattenConcOperator.prototype._e=function(err){this.out._e(err)};FlattenConcOperator.prototype._c=function(){this.less()};return FlattenConcOperator}();exports.FlattenConcOperator=FlattenConcOperator;var FInner=function(){function FInner(out,op){this.out=out;this.op=op}FInner.prototype._n=function(t){this.out._n(t)};FInner.prototype._e=function(err){this.out._e(err)};FInner.prototype._c=function(){this.op.curr=null;this.op.less()};return FInner}();var FlattenOperator=function(){function FlattenOperator(ins){this.ins=ins;this.curr=null;this.inner=null;this.open=true;this.out=null}FlattenOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FlattenOperator.prototype._stop=function(){this.ins._remove(this);this.curr=null;this.inner=null;this.open=true;this.out=null};FlattenOperator.prototype.cut=function(){var _a=this,curr=_a.curr,inner=_a.inner;if(curr&&inner){curr._remove(inner)}};FlattenOperator.prototype.less=function(){if(!this.open&&!this.curr){this.out._c()}};FlattenOperator.prototype._n=function(s){this.cut();(this.curr=s)._add(this.inner=new FInner(this.out,this))};FlattenOperator.prototype._e=function(err){this.out._e(err)};FlattenOperator.prototype._c=function(){this.open=false;this.less()};return FlattenOperator}();exports.FlattenOperator=FlattenOperator;var FoldOperator=function(){function FoldOperator(f,seed,ins){this.f=f;this.seed=seed;this.ins=ins;this.out=null;this.acc=seed}FoldOperator.prototype._start=function(out){this.out=out;out._n(this.acc);this.ins._add(this)};FoldOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.acc=this.seed};FoldOperator.prototype._n=function(t){try{this.out._n(this.acc=this.f(this.acc,t))}catch(e){this.out._e(e)}};FoldOperator.prototype._e=function(err){this.out._e(err)};FoldOperator.prototype._c=function(){this.out._c()};return FoldOperator}();var LastOperator=function(){function LastOperator(ins){this.ins=ins;this.out=null;this.has=false;this.val=empty}LastOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};LastOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.has=false;this.val=empty};LastOperator.prototype._n=function(t){this.has=true;this.val=t};LastOperator.prototype._e=function(err){this.out._e(err)};LastOperator.prototype._c=function(){var out=this.out;if(this.has){out._n(this.val);out._c()}else{out._e("TODO show proper error")}};return LastOperator}();var MFCInner=function(){function MFCInner(out,op){this.out=out;this.op=op}MFCInner.prototype._n=function(t){this.out._n(t)};MFCInner.prototype._e=function(err){this.out._e(err)};MFCInner.prototype._c=function(){this.op.less()};return MFCInner}();var MapFlattenConcOperator=function(){function MapFlattenConcOperator(mapOp){this.mapOp=mapOp;this.active=1;this.out=null}MapFlattenConcOperator.prototype._start=function(out){this.out=out;this.mapOp.ins._add(this)};MapFlattenConcOperator.prototype._stop=function(){this.mapOp.ins._remove(this);this.active=1;this.out=null};MapFlattenConcOperator.prototype.less=function(){if(--this.active===0){this.out._c()}};MapFlattenConcOperator.prototype._n=function(v){this.active++;try{this.mapOp.project(v)._add(new MFCInner(this.out,this))}catch(e){this.out._e(e)}};MapFlattenConcOperator.prototype._e=function(err){this.out._e(err)};MapFlattenConcOperator.prototype._c=function(){this.less()};return MapFlattenConcOperator}();var MFInner=function(){function MFInner(out,op){this.out=out;this.op=op}MFInner.prototype._n=function(t){this.out._n(t)};MFInner.prototype._e=function(err){this.out._e(err)};MFInner.prototype._c=function(){this.op.curr=null;this.op.less()};return MFInner}();var MapFlattenOperator=function(){function MapFlattenOperator(mapOp){this.mapOp=mapOp;this.curr=null;this.inner=null;this.open=true;this.out=null}MapFlattenOperator.prototype._start=function(out){this.out=out;this.mapOp.ins._add(this)};MapFlattenOperator.prototype._stop=function(){this.mapOp.ins._remove(this);this.curr=null;this.inner=null;this.open=true;this.out=null};MapFlattenOperator.prototype.cut=function(){var _a=this,curr=_a.curr,inner=_a.inner;if(curr&&inner){curr._remove(inner)}};MapFlattenOperator.prototype.less=function(){if(!this.open&&!this.curr){this.out._c()}};MapFlattenOperator.prototype._n=function(v){this.cut();try{(this.curr=this.mapOp.project(v))._add(this.inner=new MFInner(this.out,this))}catch(e){this.out._e(e)}};MapFlattenOperator.prototype._e=function(err){this.out._e(err)};MapFlattenOperator.prototype._c=function(){this.open=false;this.less()};return MapFlattenOperator}();var MapOperator=function(){function MapOperator(project,ins){this.project=project;this.ins=ins;this.out=null}MapOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};MapOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};MapOperator.prototype._n=function(t){try{this.out._n(this.project(t))}catch(e){this.out._e(e)}};MapOperator.prototype._e=function(err){this.out._e(err)};MapOperator.prototype._c=function(){this.out._c()};return MapOperator}();var FilterMapOperator=function(){function FilterMapOperator(predicate,project,ins){this.predicate=predicate;this.project=project;this.ins=ins;this.out=null}FilterMapOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};FilterMapOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};FilterMapOperator.prototype._tryCatch=function(v){try{this.out._n(this.project(v))}catch(e){this.out._e(e)}};FilterMapOperator.prototype._n=function(v){if(this.predicate(v)){this._tryCatch(v)}};FilterMapOperator.prototype._e=function(e){this.out._e(e)};FilterMapOperator.prototype._c=function(){this.out._c()};return FilterMapOperator}();var MapToOperator=function(){function MapToOperator(val,ins){this.val=val;this.ins=ins;this.out=null}MapToOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};MapToOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};MapToOperator.prototype._n=function(t){this.out._n(this.val)};MapToOperator.prototype._e=function(err){this.out._e(err)};MapToOperator.prototype._c=function(){this.out._c()};return MapToOperator}();var ReplaceErrorOperator=function(){function ReplaceErrorOperator(fn,ins){this.fn=fn;this.ins=ins;this.out=empty}ReplaceErrorOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};ReplaceErrorOperator.prototype._stop=function(){this.ins._remove(this);this.out=null};ReplaceErrorOperator.prototype._n=function(t){this.out._n(t)};ReplaceErrorOperator.prototype._e=function(err){try{this.ins._remove(this);(this.ins=this.fn(err))._add(this)}catch(e){this.out._e(e)}};ReplaceErrorOperator.prototype._c=function(){this.out._c()};return ReplaceErrorOperator}();var StartWithOperator=function(){function StartWithOperator(ins,value){this.ins=ins;this.value=value;this.out=emptyListener}StartWithOperator.prototype._start=function(out){this.out=out;this.out._n(this.value);this.ins._add(out)};StartWithOperator.prototype._stop=function(){this.ins._remove(this.out);this.out=null};return StartWithOperator}();var TakeOperator=function(){function TakeOperator(max,ins){this.max=max;this.ins=ins;this.out=null;this.taken=0}TakeOperator.prototype._start=function(out){this.out=out;this.ins._add(this)};TakeOperator.prototype._stop=function(){this.ins._remove(this);this.out=null;this.taken=0};TakeOperator.prototype._n=function(t){var out=this.out;if(this.taken++<this.max-1){out._n(t)}else{out._n(t);out._c();this._stop()}};TakeOperator.prototype._e=function(err){this.out._e(err)};TakeOperator.prototype._c=function(){this.out._c()};return TakeOperator}();var Stream=function(){function Stream(producer){this._stopID=empty;this.combine=function combine(project){var streams=[];for(var _i=1;_i<arguments.length;_i++){streams[_i-1]=arguments[_i]}streams.unshift(this);return Stream.combine.apply(Stream,[project].concat(streams))};this._prod=producer;this._ils=[]}Stream.prototype._n=function(t){var len=this._ils.length;if(len===1){this._ils[0]._n(t)}else{for(var i=0;i<len;i++){this._ils[i]._n(t)}}};Stream.prototype._e=function(err){var len=this._ils.length;if(len===1){this._ils[0]._e(err)}else{for(var i=0;i<len;i++){this._ils[i]._e(err)}}this._x()};Stream.prototype._c=function(){var len=this._ils.length;if(len===1){this._ils[0]._c()}else{for(var i=0;i<len;i++){this._ils[i]._c()}}this._x()};Stream.prototype._x=function(){if(this._ils.length===0)return;if(this._prod)this._prod._stop();this._ils=[]};Stream.prototype.addListener=function(listener){listener._n=listener.next;listener._e=listener.error;listener._c=listener.complete;this._add(listener)};Stream.prototype.removeListener=function(listener){this._remove(listener)};Stream.prototype._add=function(il){this._ils.push(il);if(this._ils.length===1){if(this._stopID!==empty){clearTimeout(this._stopID);this._stopID=empty}if(this._prod)this._prod._start(this)}};Stream.prototype._remove=function(il){var _this=this;var i=this._ils.indexOf(il);if(i>-1){this._ils.splice(i,1);if(this._prod&&this._ils.length<=0){this._stopID=setTimeout(function(){return _this._prod._stop()})}}};Stream.create=function(producer){if(producer){internalizeProducer(producer)}return new Stream(producer)};Stream.createWithMemory=function(producer){if(producer){internalizeProducer(producer)}return new MemoryStream(producer)};Stream.never=function(){return new Stream({_start:noop,_stop:noop})};Stream.empty=function(){return new Stream({_start:function(il){il._c()},_stop:noop})};Stream.throw=function(err){return new Stream({_start:function(il){il._e(err)},_stop:noop})};Stream.of=function(){var items=[];for(var _i=0;_i<arguments.length;_i++){items[_i-0]=arguments[_i]}return Stream.fromArray(items)};Stream.fromArray=function(array){return new Stream(new FromArrayProducer(array))};Stream.fromPromise=function(promise){return new Stream(new FromPromiseProducer(promise))};Stream.periodic=function(period){return new Stream(new PeriodicProducer(period))};Stream.merge=function(){var streams=[];for(var _i=0;_i<arguments.length;_i++){streams[_i-0]=arguments[_i]}return new Stream(new MergeProducer(streams))};Stream.prototype.map=function(project){if(this._prod instanceof FilterOperator){var prod=this._prod;return new Stream(new FilterMapOperator(prod.predicate,project,prod.ins))}if(this._prod instanceof FilterMapOperator){var prod=this._prod;return new Stream(new FilterMapOperator(prod.predicate,compose2(project,prod.project),prod.ins))}if(this._prod instanceof MapOperator){var prod=this._prod;return new Stream(new MapOperator(compose2(project,prod.project),prod.ins))}return new Stream(new MapOperator(project,this))};Stream.prototype.mapTo=function(projectedValue){return new Stream(new MapToOperator(projectedValue,this))};Stream.prototype.filter=function(predicate){if(this._prod instanceof MapOperator){var prod=this._prod;return new Stream(new FilterMapOperator(predicate,prod.project,prod.ins))}if(this._prod instanceof FilterMapOperator){var prod=this._prod;return new Stream(new FilterMapOperator(compose2(predicate,prod.predicate),prod.project,prod.ins))}if(this._prod instanceof FilterOperator){var prod=this._prod;return new Stream(new FilterOperator(compose2(predicate,prod.predicate),prod.ins))}return new Stream(new FilterOperator(predicate,this))};Stream.prototype.take=function(amount){return new Stream(new TakeOperator(amount,this))};Stream.prototype.drop=function(amount){return new Stream(new DropOperator(amount,this))};Stream.prototype.last=function(){return new Stream(new LastOperator(this))};Stream.prototype.startWith=function(x){return new Stream(new StartWithOperator(this,x))};Stream.prototype.endWhen=function(other){return new Stream(new EndWhenOperator(other,this))};Stream.prototype.fold=function(accumulate,init){return new Stream(new FoldOperator(accumulate,init,this))};Stream.prototype.replaceError=function(replace){return new Stream(new ReplaceErrorOperator(replace,this))};Stream.prototype.flatten=function(){return new Stream(this._prod instanceof MapOperator?new MapFlattenOperator(this._prod):new FlattenOperator(this))};Stream.prototype.flattenConcurrently=function(){return new Stream(this._prod instanceof MapOperator?new MapFlattenConcOperator(this._prod):new FlattenConcOperator(this))};Stream.prototype.merge=function(other){return Stream.merge(this,other)};Stream.prototype.compose=function(operator){return operator(this)};Stream.prototype.remember=function(){return new MemoryStream(this._prod)};Stream.prototype.imitate=function(other){other._add(this)};Stream.prototype.debug=function(spy){if(spy===void 0){spy=null}return new Stream(new DebugOperator(spy,this))};Stream.prototype.shamefullySendNext=function(value){this._n(value)};Stream.prototype.shamefullySendError=function(error){this._e(error)};Stream.prototype.shamefullySendComplete=function(){this._c()};Stream.combine=function combine(project){var streams=[];for(var _i=1;_i<arguments.length;_i++){streams[_i-1]=arguments[_i]}return new Stream(new CombineProducer(project,streams))};return Stream}();exports.Stream=Stream;var MemoryStream=function(_super){__extends(MemoryStream,_super);function MemoryStream(producer){_super.call(this,producer);this._has=false}MemoryStream.prototype._n=function(x){this._val=x;this._has=true;_super.prototype._n.call(this,x)};MemoryStream.prototype._add=function(listener){if(this._has){listener._n(this._val)}_super.prototype._add.call(this,listener)};return MemoryStream}(Stream);exports.MemoryStream=MemoryStream;Object.defineProperty(exports,"__esModule",{value:true});exports.default=Stream},{}],2:[function(require,module,exports){"use strict";var core_1=require("./core");exports.Stream=core_1.Stream;exports.MemoryStream=core_1.MemoryStream;Object.defineProperty(exports,"__esModule",{value:true});exports.default=core_1.Stream},{"./core":1}]},{},[2])(2)});
\ No newline at end of file
diff --git a/perf/filter-map-fusion.js b/perf/filter-map-fusion.js
new file mode 100644
index 0000000..5a765ff
--- /dev/null
+++ b/perf/filter-map-fusion.js
@@ -0,0 +1,77 @@
+var Benchmark = require('benchmark');
+var xs = require('../lib/index').default;
+var most = require('most');
+var rx = require('rx');
+var rxjs = require('@reactivex/rxjs')
+var kefir = require('kefir');
+var bacon = require('baconjs');
+var lodash = require('lodash');
+var highland = require('highland');
+
+var runners = require('./runners');
+var kefirFromArray = runners.kefirFromArray;
+
+// Create a stream from an Array of n integers
+// filter out odds, map remaining evens by adding 1, then reduce by summing
+var n = runners.getIntArg(1000000);
+var a = new Array(n);
+for(var i = 0; i< a.length; ++i) {
+  a[i] = i;
+}
+
+var suite = Benchmark.Suite('filter -> map -> reduce ' + n + ' integers');
+var options = {
+  defer: true,
+  onError: function(e) {
+    e.currentTarget.failure = e.error;
+  }
+};
+
+suite
+  .add('xstream', function(deferred) {
+    runners.runXStream(deferred,
+      xs.fromArray(a).map(add1).filter(odd).map(add1).map(add1).filter(even).fold(sum, 0).last());
+  }, options)
+  .add('most', function(deferred) {
+    runners.runMost(deferred, most.from(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(sum, 0));
+  }, options)
+  .add('rx 5', function(deferred) {
+    runners.runRx5(deferred,
+      rxjs.Observable.from(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(sum, 0));
+  }, options)
+  .add('rx 4', function(deferred) {
+    runners.runRx(deferred, rx.Observable.fromArray(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(sum, 0));
+  }, options)
+  .add('kefir', function(deferred) {
+    runners.runKefir(deferred, kefirFromArray(a).map(add1).filter(odd).map(add1).map(add1).filter(even).scan(sum, 0).last());
+  }, options)
+  .add('bacon', function(deferred) {
+    runners.runBacon(deferred, bacon.fromArray(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(0, sum));
+  }, options)
+  .add('highland', function(deferred) {
+    runners.runHighland(deferred, highland(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(0, sum));
+  }, options)
+  .add('lodash', function() {
+    return lodash(a).map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(sum, 0);
+  })
+  .add('Array', function() {
+    return a.map(add1).filter(odd).map(add1).map(add1).filter(even).reduce(sum, 0);
+  });
+
+runners.runSuite(suite);
+
+function add1(x) {
+  return x + 1;
+}
+
+function even(x) {
+  return x % 2 === 0;
+}
+
+function odd(x) {
+  return x % 2 !== 0;
+}
+
+function sum(x, y) {
+  return x + y;
+}
diff --git a/src/core.ts b/src/core.ts
index b8c71c9..302621d 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -63,6 +63,12 @@ function invoke(f: Function, args: Array<any>) {
   }
 }
 
+function compose2(f1: (t: any) => any, f2: (t: any) => any): (t: any) => any {
+  return function composedFn(arg: any): any {
+    return f1(f2(arg));
+  };
+}
+
 export interface CombineProjectFunction {
   <T1, T2, R>(v1: T1, v2: T2): R;
   <T1, T2, T3, R>(v1: T1, v2: T2, v3: T3): R;
@@ -1192,6 +1198,14 @@ export class Stream<T> implements InternalListener<T> {
       const prod = (<FilterOperator<T>> this._prod);
       return new Stream<U>(new FilterMapOperator(prod.predicate, project, prod.ins));
     }
+    if (this._prod instanceof FilterMapOperator) {
+      const prod = (<FilterMapOperator<T, T>> this._prod);
+      return new Stream<U>(new FilterMapOperator(prod.predicate, compose2(project, prod.project), prod.ins));
+    }
+    if (this._prod instanceof MapOperator) {
+      const prod = (<MapOperator<T, T>> this._prod);
+      return new Stream<U>(new MapOperator(compose2(project, prod.project), prod.ins));
+    }
     return new Stream<U>(new MapOperator(project, this));
   }
 
@@ -1219,6 +1233,14 @@ export class Stream<T> implements InternalListener<T> {
       const prod = (<MapOperator<T, T>> this._prod);
       return new Stream<T>(new FilterMapOperator(predicate, prod.project, prod.ins));
     }
+    if (this._prod instanceof FilterMapOperator) {
+      const prod = (<FilterMapOperator<T, T>> this._prod);
+      return new Stream<T>(new FilterMapOperator(compose2(predicate, prod.predicate), prod.project, prod.ins));
+    }
+    if (this._prod instanceof FilterOperator) {
+      const prod = (<FilterOperator<T>> this._prod);
+      return new Stream<T>(new FilterOperator(compose2(predicate, prod.predicate), prod.ins));
+    }
     return new Stream<T>(new FilterOperator(predicate, this));
   }