A tree is a binary recursive data structure made up of conses and atoms: the conses are themselves also trees (sometimes called ``subtrees'' or ``branches''), and the atoms are terminal nodes (sometimes called leaves). Typically, the leaves represent data while the branches establish some relationship among that data.
caaaar caddar cdar nsubst caaadr cadddr cddaar nsubst-if caaar caddr cddadr nsubst-if-not caadar cadr cddar nthcdr caaddr cdaaar cdddar sublis caadr cdaadr cddddr subst caar cdaar cdddr subst-if cadaar cdadar cddr subst-if-not cadadr cdaddr copy-tree tree-equal cadar cdadr nsublis
Figure 14-2. Some defined names relating to trees.
220.127.116.11 General Restrictions on Parameters that must be Trees