theorem
  for s being Real holds (Rotate(s)) * (Rotate(-s)) = id TOP-REAL 2
  proof
    let s be Real;
    let p be Point of T2;
    set f = Rotate(s);
    set g = Rotate(-s);
    thus (f*g).p = f.(g.p) by FUNCT_2:15
    .= p by Th46
    .= (id T2).p;
  end;
