2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/224739We compute the two-loop crossed six-line vertex master integral with two massive lines in dimensional regularisation, and give the result up to the finite part in D-4. We focus in particular on the purely analytical calculation of the boundary condition which we derive from a three-fold Mellin-Barnes representation. We also describe how the computation of the boundary condition is used to derive three non-trivial relations among harmonic polylogarithms of the sixth root of unity.10 pages, 1 figure. References added, minor modifications. Matches published versionHigh Energy Physics - Phenomenologytext