Trees binary

Defining binary trees.

Source: The Art of Prolog

Program source code: trees_binary.pl

/*
	binary_tree(Tree) :- Tree is a binary tree.
*/
	binary_tree(void).
	binary_tree(tree(Element,Left,Right)) :-
		binary_tree(Left), binary_tree(Right).
 
%	Program 3.23: Defining binary trees