Fixer for sets.
Function:
(defun sfix (set) (declare (xargs :guard (setp set))) (let ((__function__ 'sfix)) (declare (ignorable __function__)) (mbe :logic (if (setp set) set nil) :exec (the (or cons null) set))))
Theorem:
(defthm setp-of-sfix (b* ((set$ (sfix set))) (setp set$)) :rule-classes :rewrite)