The `BST` class inherits the three member variables
`key`, `left`, and `right`
for the `BinaryTree` class.
All three of them are pointers.
The first is a pointer to an `Object` instance,
and the latter two are pointers to `BinaryTree` instances.
All three pointers are zero if the node represents the empty tree.
Otherwise, the tree must have a root and two subtrees.
Therefore, all three pointers are non-zero in an internal node.

Program defines the two member functions `Left`
and `Right` which return the left and right subtrees,
respectively, of a given binary search tree.
Since the implementation extends the `BinaryTree` class,
the `left` and `right` member variables are declared as pointers
to `BinaryTree`s.
However, in a binary search tree,
the subtrees will be instances of the `BST` class.
Therefore, these functions make use of the `dynamiccast`
operator to return a reference of the correct type.

**Program:** `BST` Class `Left` and `Right` Member Function Definitions

Copyright © 1997 by Bruno R. Preiss, P.Eng. All rights reserved.