const In : set set prop term iIn = In infix iIn 2000 2000 const SNo : set prop const SNoLt : set set prop term < = SNoLt infix < 2020 2020 term SNoCutP = \x:set.\y:set.(!z:set.z iIn x -> SNo z) & (!z:set.z iIn y -> SNo z) & !z:set.z iIn x -> !w:set.w iIn y -> z < w term nIn = \x:set.\y:set.~ x iIn y const SNoCut : set set set axiom SNoCutP_SNo_SNoCut: !x:set.!y:set.SNoCutP x y -> SNo (SNoCut x y) const SNoS_ : set set const SNoLev : set set axiom SNoLev_ind: !p:set prop.(!x:set.SNo x -> (!y:set.y iIn SNoS_ (SNoLev x) -> p y) -> p x) -> !x:set.SNo x -> p x const minus_SNo : set set term - = minus_SNo const Repl : set (set set) set lemma !x:set.!y:set.!z:set.SNo x -> (!w:set.w iIn SNoS_ (SNoLev x) -> !u:set.!v:set.SNoCutP u v -> w = SNoCut u v -> - w = SNoCut (Repl v minus_SNo) (Repl u minus_SNo)) -> SNoCutP y z -> (!w:set.w iIn y -> SNo w) -> (!w:set.w iIn z -> SNo w) -> x = SNoCut y z -> SNo (SNoCut y z) -> - x = SNoCut (Repl z minus_SNo) (Repl y minus_SNo) claim !x:set.SNo x -> !y:set.!z:set.SNoCutP y z -> x = SNoCut y z -> - x = SNoCut (Repl z \w:set.- w) (Repl y \w:set.- w)