The resolution of CWG2051, applied in 573152d, changed the condition on n in the definition of cv-decomposition for type T from n > 0 to n ≥ 0, but the example was not updated. It says that

The type denoted by the type-id const int ** has two cv-decompositions, taking U as “int” and as “pointer to const int”.

However, since n in a cv-decomposition now can be 0, it is possible to take U as “pointer to pointer to const int” and this is the third cv-decomposition for const int **.

The issue was spotted in https://stackoverflow.com/q/56733770/9585016