Set difference.
(diff x y) → set
Time complexity: O(n\log(m/n)) (where n < m).
Function: diff
(defun diff (x y) (declare (xargs :guard (and (setp x) (setp y)))) (tree-diff (sfix x) (sfix y)))
Theorem: setp-of-diff
(defthm setp-of-diff (b* ((set (diff x y))) (setp set)) :rule-classes :rewrite)