reserve P,Q,X,Y,Z for set, p,x,x9,x1,x2,y,z for object;

theorem Th8:
  for f being Function of X,Y st Y = {} implies X = {} holds f in Funcs(X,Y)
proof
  let f be Function of X,Y;
  assume Y = {} implies X = {};
  then
A1: dom f = X by Def1;
  rng f c= Y;
  hence thesis by A1,Def2;
end;
