2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/77183Let X be a (possibly nodal) K-trivial threefold moving in a fixed ambient space P. Suppose X contains a continuous family of curves, all of whose members satisfy certain unobstructedness conditions in P. A formula is given for computing the corresponding virtual number of curves, that is, the number of curves on a generic deformation of X "contributed by" the continuous family on X.25 pages, LaTeX2e. Several minor corrections and clairifications; theorem 3.3. slighlty strengthened; references updatedAlgebraic Geometry14C05, 14H10, 14J32, 14N10 (Primary) 14C17, 14D15, 14F10 (Secondary)text