2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/227131We consider d=4, N=2 compactifications of heterotic strings with an arbitrary number of Wilson lines. In particular, we focus on known chains of candidate heterotic/type II duals. We give closed expressions for the topological amplitudes F^g in terms of automorphic forms of SO(2+k,2,Z), and find agreement with the geometric data of the dual K3 fibrations wherever those are known.34 pages, 8 figures; typos corrected, references addedHigh Energy Physics - Theorytext