reserve i,j,k for Nat;

theorem Th4:
  for K being commutative left_unital non empty multLoopStr holds
  1.K is_a_unity_wrt the multF of K
proof
  let K be commutative left_unital non empty multLoopStr;
  set o = the multF of K;
  now
    let h be Element of K;
    thus o.(1.K,h) = 1.K * h .= h;
    thus o.(h,1.K) = h * 1.K .= h;
  end;
  hence thesis by BINOP_1:3;
end;
