84 element_type e1, element_type e2, element_type e3) {
87 std::map<element_type, std::map<element_type, triple_type *>>>::iterator
89 iter1 = triple_map_.find(e1);
90 if (iter1 == triple_map_.end()) {
94 typename std::map<element_type,
95 std::map<element_type, triple_type *>>::iterator iter2;
96 iter2 = iter1->second.find(e2);
97 if (iter2 == iter1->second.end()) {
101 typename std::map<element_type, triple_type *>::iterator iter3;
102 iter3 = iter2->second.find(e3);
103 if (iter3 == iter2->second.end()) {
107 return iter3->second;