StringSet operator + (const StringSet& ss1, const StringSet& ss2){
	StringSet merged;
	for (size_t i = 0; i < ss1.size(); ++i)
		merged.addString(ss1.at(i));
	for (size_t i = 0; i < ss2.size(); ++i)
		merged.addString(ss2.at(i));
    return merged;
}
StringSet operator * (const StringSet& ss1, const StringSet& ss2){
	StringSet intersection;
    for (size_t i = 0; i < ss1.size(); ++i){
    	for (size_t j = 0; j < ss2.size(); ++j){
    		if (ss1.at(i) == ss2.at(j))
    			intersection.addString(ss2.at(j));
    	}
    }
    return intersection;
}