2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/73983We prove various results on contact structures obtained by contact surgery on a single Legendrian knot in the standard contact three--sphere. Our main tool are the contact Ozsvath--Szabo invariants.15 pages, 10 figures. Small changes, references addedSymplectic GeometryGeometric Topologytext