When comparing two objects with different definitions of the operator==() function, which definition is used?

Suppose there are two objects of different classes, and they are being compared with each other. Both classes overload the operator==() function, but in different ways. What will the result of the comparison be?

class A
{
  bool operator==( const A &lhs, const B &rhs ){ return true; };
  bool operator==( const B &lhs, const A &rhs ){ return true; };
};

class B
{
  bool operator==( const A &lhs, const B &rhs ){ return false; };
  bool operator==( const B &lhs, const A &rhs ){ return false; };
};

int main( int argc, char **argv )
{
  A a();
  B b();
  assert( a == b ); //What's the result?
};