
theorem Th4:
  for A,B,x being set, f being Function st x in A & f in Funcs(A,B)
  holds f.x in B
proof
  let A,B,x be set, f be Function such that
A1: x in A;
  assume
A2: f in Funcs(A,B);
  then
A3: f is Function of A,B by FUNCT_2:66;
  B = {} implies A = {} by A2;
  hence thesis by A1,A3,FUNCT_2:5;
end;
