prop.gd: add "condition true → property false" implications

digraphs · Nov 22, 2021 · 2f59a34 · 2f59a34
1 parent fd6bba1
commit 2f59a34
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Showing 2 changed files with 44 additions and 2 deletions.
diff --git a/gap/prop.gd b/gap/prop.gd
@@ -108,3 +108,45 @@ InstallTrueMethod(IsNonemptyDigraph, IsDigraph and DigraphHasLoops);
 InstallTrueMethod(DigraphHasLoops, IsReflexiveDigraph and DigraphHasAVertex);
 InstallTrueMethod(DigraphHasAVertex, IsDigraph and IsNonemptyDigraph);
 InstallTrueMethod(DigraphHasAVertex, IsDigraph and IsDirectedTree);
+
+# Implications that something is false
+
+InstallTrueMethod(HasDigraphHasLoops, IsAcyclicDigraph);
+InstallTrueMethod(HasDigraphHasLoops, IsTournament);
+InstallTrueMethod(HasDigraphHasLoops, IsUndirectedForest);
+InstallTrueMethod(HasDigraphHasLoops, IsDirectedTree);
+InstallTrueMethod(HasDigraphHasLoops, IsEmptyDigraph);
+InstallTrueMethod(HasDigraphHasLoops, IsCompleteDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasDigraphHasLoops, IsBipartiteDigraph);
+
+# The following are usually redundant because of immediate methods
+InstallTrueMethod(HasIsNonemptyDigraph, IsEmptyDigraph);
+InstallTrueMethod(HasIsEmptyDigraph, IsDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasDigraphHasAVertex, DigraphHasNoVertices);
+InstallTrueMethod(HasDigraphHasNoVertices, DigraphHasAVertex);
+
+InstallTrueMethod(HasIsAcyclicDigraph, IsCompleteDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasIsAcyclicDigraph, IsDigraph and DigraphHasLoops);
+InstallTrueMethod(HasIsAcyclicDigraph,
+                  IsStronglyConnectedDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasIsAntisymmetricDigraph,
+                  IsCompleteDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasIsChainDigraph, IsDigraph and DigraphHasLoops);
+InstallTrueMethod(HasIsChainDigraph, IsSymmetricDigraph and IsNonemptyDigraph);
+InstallTrueMethod(HasIsCompleteDigraph, IsDigraph and DigraphHasLoops);
+InstallTrueMethod(HasIsReflexiveDigraph,
+                  IsAcyclicDigraph and DigraphHasAVertex);
+
+InstallTrueMethod(HasIsSymmetricDigraph, IsAcyclicDigraph
+                                         and IsNonemptyDigraph);
+InstallTrueMethod(HasIsSymmetricDigraph, IsDirectedTree and IsNonemptyDigraph);
+InstallTrueMethod(HasIsSymmetricDigraph, IsTournament and IsNonemptyDigraph);
+
+InstallTrueMethod(HasIsMultiDigraph, IsChainDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsCompleteDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsCompleteMultipartiteDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsCycleDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsEmptyDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsFunctionalDigraph);
+InstallTrueMethod(HasIsMultiDigraph, IsTournament);
+InstallTrueMethod(HasIsMultiDigraph, IsUndirectedForest);
diff --git a/tst/standard/prop.tst b/tst/standard/prop.tst
@@ -1,7 +1,7 @@
 #############################################################################
 ##
 #W  standard/prop.tst
-#Y  Copyright (C) 2014-17                                James D. Mitchell
+#Y  Copyright (C) 2014-21                                James D. Mitchell
 ##                                                          Wilf A. Wilson
 ##
 ##  Licensing information can be found in the README file of this package.
@@ -139,7 +139,7 @@ gap> gr := Digraph([[1]]);;
 gap> DigraphHasLoops(gr);
 true
 gap> HasIsAcyclicDigraph(gr);
-false
+true
 gap> IsAcyclicDigraph(gr);
 false
 gap> gr := Digraph([[2], []]);