proposition: Lemma cantor_bis_alt: non_coll cardinalp.
proof: Proof. move=> [a ap]. set (s:= union a). set (e:= cardinal s). have cp:= CS_pow \2c e. case: (cltNge (cantor (CS_cardinal s))). have /sub_smaller : (sub (\2c ^c e) s) by apply: setU_s1; apply/ ap. by rewrite (card_card cp). Qed.
imports: mathcomp(ssreflect ssrbool eqtype ssrfun)