theorem
  for h,k being Real holds
  exp_R(h-k) = exp_R(h) / exp_R(k)
proof
  let h,k be Real;
  exp_R(h-k) = exp_R(h) * exp_R(-k) by SIN_COS:50
    .= exp_R(h)*(1/exp_R(k)) by TAYLOR_1:4
    .= exp_R(h) / exp_R(k);
  hence thesis;
end;
