1 (defun generate-huffman-tree (pairs)
2   (successive-merge (make-leaf-set pairs)))
3 (defun successive-merge (node-set)
4   (if (null (cadr node-set))
5       (car node-set)
6       (successive-merge
7        (adjoin-set (make-code-tree (car node-set)
8 				   (cadr node-set))
9 		   (cddr node-set)))))