signature ComplexSig =
sig
   type complex;

   val descartes : {real    : real, imag     : real} -> complex
   and argand    : {modulus : real, argument : real} -> complex

   and ++ : complex * complex -> complex
   and -- : complex * complex -> complex
   and ** : complex * complex -> complex
   and // : complex * complex -> complex
   and X  : real    * complex -> complex
   and == : complex * complex -> bool

   and ~~      : complex -> complex
   and modulus : complex -> real
   and argument: complex -> real
   and realpart: complex -> real
   and imagpart: complex -> real
end;