public static Object copy_tree(Object tree) {
if ( consp(tree) )
return cons(copy_tree(first((Cons) tree)),
(Cons) copy_tree(rest( (Cons) tree)));
return tree; }
public static Object
subst(Object gnew, String old, Object tree) {
if ( consp(tree) )
return cons(subst(gnew, old,
first((Cons) tree)),
(Cons) subst(gnew, old,
rest((Cons) tree)));
return (old.equals(tree)) ? gnew : tree; }