theorem Th15:
  for f being Function of A,B st B = {} implies A = {} holds [[A,B
  ],f] in Maps(A,B)
proof
  let f be Function of A,B;
  assume B = {} implies A = {};
  then f in Funcs(V) & [[A,B],f] in Maps(V) by Th1,Th5;
  hence thesis;
end;
