theorem
  Hom(C) c= V implies hom??(V,C).[f opp,g] = [[Hom(cod f,dom g),Hom(dom
  f,cod g)],hom(f,g)]
proof
  assume
A1: Hom(C) c= V;
  thus (hom??(V,C)).[f opp,g] = (hom??(C)).[f,g] by A1,Def26
    .= [[Hom(cod f,dom g),Hom(dom f,cod g)],hom(f,g)] by Def23;
end;
