const In : set set prop term iIn = In infix iIn 2000 2000 term nIn = \x:set.\y:set.~ x iIn y const SNo : set prop const SNoLt : set set prop term < = SNoLt infix < 2020 2020 axiom SNoLt_tra: !x:set.!y:set.!z:set.SNo x -> SNo y -> SNo z -> x < y -> y < z -> x < z axiom SNoLt_irref: !x:set.~ x < x const SNoLev : set set const eps_ : set set const Empty : set var x:set var y:set var z:set hyp Empty < y hyp SNo y hyp SNo z hyp y < z hyp SNoLev z iIn eps_ x claim z != Empty