I only stumbled to this problem recently, after happily using the patently unportable solution for years (with numerous versions of STL to boot). Let's say we have a sorted vector of complex objects with a fairly simple key, and want to do lower_bound() on just a key, not a specially constructed instance of the whole object. It turns out that: bool less( const Object&, const Key& ); lower_bound( v.begin(), v.end(), Key(something), ptr_fun(less) ); is expressly prohibited by the SGI STL specifications and not quite allowed, even though not quite prohibited either, by the ISO standard (unless my standardese grew rusty again). It also turns out that there are STLs where it won't work (e.g. the new Plauger's STL shipped with VStudio 2005 release, but not beta 2...). Now, this: struct less { bool operator()( const Object&, const Key& ) const; bool operator()( const Key&, const Object& ) const; }; lower_bound( v.begin(), v.end(), Key(something), less() ); should work everywhere, or so I think. Would be nice to be able to create such an adaptor for a pair of functions (or a pair of bind or lambda expressions for that matter). I blogged a simple solution (for functions only) here http://swsw.motovilov.net/weblogs/swsw/archives/2006/02/asymmetrical_pr.html but am wondering if perhaps I missed a generic solution in one of the Boost libraries, or there's one coming in the new release? Any comments/suggestions? Regards, ...Max...