diff --git a/chapter6/sections/4/1.tex b/chapter6/sections/4/1.tex
index a0deb8f..0f71820 100644
--- a/chapter6/sections/4/1.tex
+++ b/chapter6/sections/4/1.tex
@@ -1 +1,24 @@
-\workinprogress % TODO
+See \refFigure{6.4-1}.
+\begin{figure}[htb]
+    \hspace*{-1.5cm}
+    \begin{minipage}{\textwidth + 1.5cm}
+        \captionsetup[subfigure]{}
+        \subcaptionbox{\label{fig:6.4-1a}}[0.33\textwidth]{\input{1a.tikz}}
+        \subcaptionbox{\label{fig:6.4-1b}}[0.33\textwidth]{\input{1b.tikz}}
+        \subcaptionbox{\label{fig:6.4-1c}}[0.33\textwidth]{\input{1c.tikz}}
+        \par\vspace{3ex}
+        \subcaptionbox{\label{fig:6.4-1d}}[0.33\textwidth]{\input{1d.tikz}}
+        \subcaptionbox{\label{fig:6.4-1e}}[0.33\textwidth]{\input{1e.tikz}}
+        \subcaptionbox{\label{fig:6.4-1f}}[0.33\textwidth]{\input{1f.tikz}}
+        \par\vspace{3ex}
+        \subcaptionbox{\label{fig:6.4-1g}}[0.33\textwidth]{\input{1g.tikz}}
+        \subcaptionbox{\label{fig:6.4-1h}}[0.33\textwidth]{\input{1h.tikz}}
+        \subcaptionbox{\label{fig:6.4-1i}}[0.33\textwidth]{\input{1i.tikz}}
+        \par\vspace{3ex}
+        \subcaptionbox{\label{fig:6.4-1j}}[0.33\textwidth]{\input{1j.tikz}}
+    \end{minipage}
+    \caption{The operation of \proc{Heapsort} on the array $A=\langle$5, 13, 2, 25, 7, 17, 20, 8, 4$\rangle$.\,
+    \textbf{(a)}\, The max-heap built by \proc{Build-Max-Heap} in line 1.\,
+    \textbf{(b)--(i)}\, The max-heap and the nodes removed from it after each call to \proc{Max-Heapify} in line 5.\,
+    \textbf{(j)}\, The resulting sorted array $A$.} \label{fig:6.4-1}
+\end{figure}
diff --git a/chapter6/sections/4/1.tikz b/chapter6/sections/4/1.tikz
new file mode 100644
index 0000000..774c2d5
--- /dev/null
+++ b/chapter6/sections/4/1.tikz
@@ -0,0 +1,7 @@
+\setlength{\vertexsize}{1.1em}
+\tikzset{
+    every node/.style = {light blue vertex},
+    discarded/.style = {tan vertex},
+    every label/.style = {index},
+    level/.append style = {sibling distance=5\vertexsize/#1},
+}
diff --git a/chapter6/sections/4/1a.tikz b/chapter6/sections/4/1a.tikz
new file mode 100644
index 0000000..304eca6
--- /dev/null
+++ b/chapter6/sections/4/1a.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {25}
+        child {node {13}
+            child {node {8}
+                child {node {5}}
+                child {node {4}}
+            }
+            child {node {7}}
+        }
+        child {node {20}
+            child {node {17}}
+            child {node {2}
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1b.tikz b/chapter6/sections/4/1b.tikz
new file mode 100644
index 0000000..ce9bb30
--- /dev/null
+++ b/chapter6/sections/4/1b.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {20}
+        child {node {13}
+            child {node {8}
+                child {node {5}}
+                child {node[discarded, label=right:{$i$}] {25} edge from parent[draw=none]}
+            }
+            child {node {7}}
+        }
+        child {node {17}
+            child {node {4}}
+            child {node {2}
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1c.tikz b/chapter6/sections/4/1c.tikz
new file mode 100644
index 0000000..0ebb750
--- /dev/null
+++ b/chapter6/sections/4/1c.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {17}
+        child {node {13}
+            child {node {8}
+                child {node[discarded, label=left:{$i$}] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node {7}}
+        }
+        child {node {5}
+            child {node {4}}
+            child {node {2}
+                child[missing]
+                child {node[draw=none, fill=none, label=right:{}] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1d.tikz b/chapter6/sections/4/1d.tikz
new file mode 100644
index 0000000..33f2f77
--- /dev/null
+++ b/chapter6/sections/4/1d.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {13}
+        child {node {8}
+            child {node {2}
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node {7}}
+        }
+        child {node {5}
+            child {node {4}}
+            child {node[discarded, label=left:{$i$}] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1e.tikz b/chapter6/sections/4/1e.tikz
new file mode 100644
index 0000000..7be7bcf
--- /dev/null
+++ b/chapter6/sections/4/1e.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {8}
+        child {node {7}
+            child {node {2}
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node {4}}
+        }
+        child {node {5}
+            child {node[discarded, label=left:{$i$}] {13} edge from parent[draw=none]}
+            child {node[discarded] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1f.tikz b/chapter6/sections/4/1f.tikz
new file mode 100644
index 0000000..45607b1
--- /dev/null
+++ b/chapter6/sections/4/1f.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {7}
+        child {node {4}
+            child {node {2}
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node[discarded, label=left:{$i$}] {8} edge from parent[draw=none]}
+        }
+        child {node {5}
+            child {node[discarded] {13} edge from parent[draw=none]}
+            child {node[discarded] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1g.tikz b/chapter6/sections/4/1g.tikz
new file mode 100644
index 0000000..5f11893
--- /dev/null
+++ b/chapter6/sections/4/1g.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {5}
+        child {node {4}
+            child {node[discarded, label=left:{$i$}] {7} edge from parent[draw=none]
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node[discarded] {8} edge from parent[draw=none]}
+        }
+        child {node {2}
+            child {node[discarded] {13} edge from parent[draw=none]}
+            child {node[discarded] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1h.tikz b/chapter6/sections/4/1h.tikz
new file mode 100644
index 0000000..ecca8ce
--- /dev/null
+++ b/chapter6/sections/4/1h.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {4}
+        child {node {2}
+            child {node[discarded] {7} edge from parent[draw=none]
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node[discarded] {8} edge from parent[draw=none]}
+        }
+        child {node[discarded, label=left:{$i$}] {5} edge from parent[draw=none]
+            child {node[discarded] {13} edge from parent[draw=none]}
+            child {node[discarded] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1i.tikz b/chapter6/sections/4/1i.tikz
new file mode 100644
index 0000000..29d2e8c
--- /dev/null
+++ b/chapter6/sections/4/1i.tikz
@@ -0,0 +1,18 @@
+\input{1.tikz}
+\begin{tikzpicture}
+    \node {2}
+        child {node[discarded, label=left:{$i$}] {4} edge from parent[draw=none]
+            child {node[discarded] {7} edge from parent[draw=none]
+                child {node[discarded] {20} edge from parent[draw=none]}
+                child {node[discarded] {25} edge from parent[draw=none]}
+            }
+            child {node[discarded] {8} edge from parent[draw=none]}
+        }
+        child {node[discarded] {5} edge from parent[draw=none]
+            child {node[discarded] {13} edge from parent[draw=none]}
+            child {node[discarded] {17} edge from parent[draw=none]
+                child[missing]
+                child {node[draw=none, fill=none] {} edge from parent[draw=none]}
+            }
+        };
+\end{tikzpicture}
diff --git a/chapter6/sections/4/1j.tikz b/chapter6/sections/4/1j.tikz
new file mode 100644
index 0000000..9cb3f72
--- /dev/null
+++ b/chapter6/sections/4/1j.tikz
@@ -0,0 +1,7 @@
+\input{1.tikz}
+\begin{tikzpicture}[
+    every node/.style = {},
+]
+    \matrix[array, row 1/.append style={nodes={fill=tan}}, label=left:{$A$}] {
+            2 & 4 & 5 & 7 & 8 & 13 & 17 & 20 & 25 \\};
+\end{tikzpicture}