public T Foo<T>(Whatever<T> param) where T : (+), (-), (*), (/) {
 ...
}

##</code><code>##

// in Clean
foo:: a a a -> a | Arith a
foo x y z = x + y * z

// in C#
public T foo<T>(T x, T y, T z) where T : IArith {
  return x + y * z;
}