(set-logic QF_UF)
(declare-sort S 0)
(declare-fun f (S) S)
(declare-fun g (S) S)
(declare-fun x1 () S)
(declare-fun x2 () S)
(assert (= (f (g x1)) (g (f (f x2)))))
(assert (= (f x1) (g x2)))
(check-sat)