2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148324We review two different methods of calculating Witten's invariant: a stationary phase approximation and a surgery calculus. We give a detailed description of the 1-loop approximation formula for Witten's invariant and of the technics involved in deriving its exact value through a surgery construction of a manifold. Finally we compare the formulas produced by both methods for a 3-dimensional sphere S^3 and a lens space L(p,1).29 pages, "\draft" declaration has been removedHigh Energy Physics - TheoryQuantum Algebratext