Consider the namespace and function definitions below. In which of the following cases would a new function declaration overloading of f

be invalid?

namespace a {
  int f(int x, int y = 3) { return x + y; }
}
namespace b {
  int f(int x=1) { return x + 1; }
  double f(int x, double y) { return x + y; }
}
int f(int x) {
  return x;
}