Equivalence up to sfix.
Function:
(defun set-equiv$inline (x y) (declare (xargs :guard (and (setp x) (setp y)))) (declare (xargs :type-prescription (booleanp (set-equiv x y)))) (equal (sfix x) (sfix y)))
Theorem:
(defthm set-equiv-is-an-equivalence (and (booleanp (set-equiv x y)) (set-equiv x x) (implies (set-equiv x y) (set-equiv y x)) (implies (and (set-equiv x y) (set-equiv y z)) (set-equiv x z))) :rule-classes (:equivalence))