2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/75591We shall prove that any small deformation of a Q-factorial projective symplectic variety with terminal singularities is locally rigid; in other words, it preserves the singularity. In particular, many singular symplectic moduli of semi-stable sheaves on K3 have no smoothings via deformations. As an application of the result, we also prove that the smootheness is preserved under a flop in our symplectic case. We conjecture that a projective symplectic variety has a smoothing by a flat deformation if and only if it has a crepant (symplectic) resolution. This conjecture would be true if the minimal model conjecture were true.Some details and explanations are added. To appear in CrelleAlgebraic Geometry14, 32text