template<int x> struct A {
template<int y> struct B {};.
template<int y, int unused> struct C {};
};
template<int x> template<>
struct A<x>::B<x> {}; // error: enclosing class templates are not explicitly specialized
template<int x> template<int unused>
struct A<x>::C<x, unused> {}; // ok
template<int x> struct A {