const ordinal : set prop const In : set set prop term iIn = In infix iIn 2000 2000 axiom ordinal_Hered: !x:set.ordinal x -> !y:set.y iIn x -> ordinal y const add_SNo : set set set term + = add_SNo infix + 2281 2280 lemma !x:set.!y:set.!z:set.ordinal x -> ordinal y -> z iIn x -> ordinal z -> z + y iIn x + y claim !x:set.ordinal x -> !y:set.ordinal y -> !z:set.z iIn x -> z + y iIn x + y