Header file for functions inside of a namespace?

Question

In C++ I have a file A.cpp that has the following in it:

 namespace Foo {

     bool Bar() 
     { 
         return true; 
     }

 }

How would I declare this function in A.h? How do I handle the namespace?

Answer 1

namespace Foo {
  bool Bar();
}

Answer 2

namespace Foo {
    bool Bar();
}

Answer 3

namespace Foo {
    bool Bar();
}

Or

namespace Foo;
bool Foo::Bar();

Answer 4

namespace Foo {
    bool Bar();
}