len (the_arity_of (@ set-constr)) = card ((set-constr `2) `1) by ABCMIZ_1:def 24
.= card ([{},0] `1) by MCART_1:7
.= card 0 by MCART_1:7 ;
hence the_arity_of (@ set-constr) = {} ; :: according to ABCMIZ_A:def 13 :: thesis: verum