message: complex cotangent function
diff: @@ -201,6 +201,11 @@ template <typename T> Complex<T> tan(const Complex<T> &z) {
  return s / c;
  }
  +template <typename T> Complex<T> cot(const Complex<T> &z) {
  + auto [s, c] = sincos(z);
  + return c / s;
  +}
  +
  template <typename T>
  Complex<T> asin(const Complex<T> &z) {
  Complex<T> tmp = log(Complex<T>(-imag(z), real(z)) + sqrt(1.f - sqr(z)));
  