reserve X,Y,Z,X1,X2,Y1,Y2 for set, x,y,z,t,x1,x2 for object,
  f,g,h,f1,f2,g1,g2 for Function;

theorem Th50:
  Funcs({},X) = {{}}
proof
  thus Funcs({},X) c= {{}}
  proof
    let x be object;
    assume x in Funcs({},X);
    then ex f st x = f & dom f = {} & rng f c= X by FUNCT_2:def 2;
    then x = {};
    hence thesis by TARSKI:def 1;
  end;
  let x be object;
A1: {} c= X;
  assume x in {{}};
  then
A2: x = {} by TARSKI:def 1;
  dom {} = {} & rng {} = {};
  hence thesis by A2,A1,FUNCT_2:def 2;
end;
