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