Hi: I have the following code: struct VectorComp { bool operator()(const std::vector<std::bitset<6>>& lhs, const std::vector<std::bitset<6>>& rhs) const { return false; } }; typedef boost::bimaps::bimap<boost::bimaps::set_of<std::vector<std::bitset<6>>, VectorComp>, int> SignsList_Type; SignsList_Type SignsList; When compiling this code, I get c2676 errors from visual studio: 8 error C2676: binary '<' : 'const std::bitset<_Bits>' does not define this operator or a conversion to a type acceptable to the functional 143 I have BitsetComp which successfully compares two std::bitsets. How do I insert this so that my code works succesfully? Cheers Sean. __________ Information from ESET NOD32 Antivirus, version of virus signature database 3421 (20080906) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com