A characterization of Ext(G, ℤ) assuming (V = L)

We complete the characterization of Ext(G, ℤ) for any torsion-free abelian group G assuming Gödel's axiom of constructibility plus there is no weakly compact cardinal. In particular, we prove in (V = L) that, for a singular cardinal v of uncountable cofinality which is less than the first weakly compact cardinal and for every sequence (v_p : p ∈ ∏) of cardinals satisfying v_p ≤ 2^v (where ∏ is the set of all primes), there is a torsion-free abelian group G of size v such that v_p equals the p-rank of Ext(G, ℤ) for every prime p and 2 ^v is the torsion-free rank of Ext(G, ℤ).