#include <iostream>#include <boost/numeric/linear_algebra/operators.hpp>#include <boost/numeric/linear_algebra/identity.hpp>#include <boost/numeric/linear_algebra/concepts.hpp>#include <libs/numeric/linear_algebra/test/algebraic_functions.hpp>using math::identity; using math::add;using std::string;namespace math {    template<>     struct identity_t< math::add<string>, string >      {         string operator()(const math::add<string>&, const string&) const         {	    return string();         }     } ;# ifdef __GXX_CONCEPTS__    concept_map Monoid< math::add<string>, string > {}# endif // __GXX_CONCEPTS__}        int main(int, char* []) {    using namespace std;    using namespace mtl;    string               sa("a"), sab("ab"), sbc("bc"), sc("c"), s;    math::add<string>    string_add;    cout << "equal_results(sa, sbc,  sab, sc, string_add) " 	 << equal_results(sa, sbc,  sab, sc, string_add)  << endl;    cout << "equal_results(sab, sbc,  sab, sc, string_add) " 	 << equal_results(sab, sbc,  sab, sc, string_add) << endl;        cout << "identity_pair(s, s, string_add) " 	 << identity_pair(s, s, string_add)  << endl;    cout << "identity_pair(sa, sa, string_add) " 	 << identity_pair(sa, sa, string_add)  << endl;    cout << "multiply_and_square(sab, 13, string_add) "	 << multiply_and_square(sab, 13, string_add) << endl;    return 0;}