AbstractLet p be a prime and F a field containing a primitive p-th root of unity. Then for n ∈ N, the cohomological dimension of the maximal pro-p-quotient G of the absolute Galois group of F is at most n if and only if the corestriction maps are surjective for all open subgroups H of index p. Using this result, we generalize Schreier's formula for .