const In : set set prop term iIn = In infix iIn 2000 2000 term Subq = \x:set.\y:set.!z:set.z iIn x -> z iIn y const SNo : set prop const minus_SNo : set set term - = minus_SNo axiom SNo_minus_SNo: !x:set.SNo x -> SNo - x const SNoL : set set const Repl : set (set set) set const SNoR : set set lemma !x:set.SNo x -> SNo - x -> SNoL - x = Repl (SNoR x) minus_SNo claim !x:set.SNo x -> SNoL - x = Repl (SNoR x) minus_SNo