\chapter{Binary trees}
\label{chap-binary-trees}

\Defclass {node}

This class is the base class for all node types in binary trees.

\Defgeneric {left} {node}

Given a node, return the left child of that node.

\Defclass {simple-node}

This class is a subclass of the class \texttt{node}.  It does not add
any slots, and is only meant for client code to be able to distinguish
between a node with a parent and a node without one.

\Defclass {node-with-parent}

This class is a subclass of the class \texttt{node}.  It adds a slot
for storing a reference to the parent node in a binary tree.

\chapter{Binary trees}
\label{chap-binary-trees}

\Defclass {node}

This class is the base class for all node types in binary trees.

\Defgeneric {left} {node}

Given a node, return the left child of that node.  The value returned
by this function may be either an instance of (a subclass of) the
class \texttt{node} or \texttt{nil} if the left child of \textit{node}
is the empty tree.

\Defclass {simple-node}

This class is a subclass of the class \texttt{node}.  It does not add
any slots, and is only meant for client code to be able to distinguish
between a node with a parent and a node without one.

\Defclass {node-with-parent}

This class is a subclass of the class \texttt{node}.  It adds a slot
for storing a reference to the parent node in a binary tree.

Improve description of generic function LEFT.
Improve description of generic function LEFT.
