operator overload with namespace

From: Jason C (nightcom26_at_gmail.com)
Date: 02/28/05 

Date: 28 Feb 2005 07:33:00 -0800

Hi, I am coming from C background and trying to learn C++. So bear with
me if the answer to my question is obvious.

I am trying to overload the "+" operator in different namespaces, like
this:

namespace A
{
std::string operator+(std::string const &a, std::string const &b);
}

namespace B
{
std::string operator+(std::string const &a, std::string const &b);
}

How do I explicitly call the + operator in either namespace, rather
than the + operator defined in the std::string?