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 axiom In_ind: !p:set prop.(!x:set.(!y:set.y iIn x -> p y) -> p x) -> !x:set.p x claim !p:set prop.(!x:set.ordinal x -> (!y:set.y iIn x -> p y) -> p x) -> !x:set.ordinal x -> p x