[boost] Partially specializing less<> with nested template class

This is what I would like to do: template <class P1, class P2> struct sp { template <typename T> struct nested { }; }; template <typename T> struct less; template <class P1, class P2, typename T> struct less<sp<P1, P2>::nested<T> > : binary_function<...> { bool operator()(...); }; However, it doesn't work. From my research, it seems that the problem is that T is in a non-deduced context, but I don't see why that would be an issue, since this is how I expect it to get instantiated: less<sp<p1, p2>::nested<int> > comp; Thus, I don't see any deduction as being necessary, but obviously I don't exactly understand how to get what I want. Dave