theorem
  Hom(C) c= V implies (hom?-(V,a)).f = [[Hom(a,dom f),Hom(a,cod f)],hom(
  a, f ) ]
proof
  assume Hom(C) c= V;
  hence (hom?-(V,a)).f = (hom?-(a)).f by Def24
    .= [[Hom(a,dom f),Hom(a,cod f)],hom(a,f)] by Def20;
end;
