let C be Category; for b, a being Object of C st b is terminal holds
( dom (term a,b) = a & cod (term a,b) = b )
let b, a be Object of C; ( b is terminal implies ( dom (term a,b) = a & cod (term a,b) = b ) )
assume
b is terminal
; ( dom (term a,b) = a & cod (term a,b) = b )
then
Hom a,b <> {}
by CAT_1:def 15;
hence
( dom (term a,b) = a & cod (term a,b) = b )
by CAT_1:23; verum