Tangent cones at Gorenstein singularities
Let be a numerical semigroup. We say that is an isolated gap of if A numerical semigroup without isolated gaps is called a perfect numerical semigroup. Denote by the multiplicity of a numerical semigroup . A covariety is a nonempty family of numerical semigroups that fulfills the following conditions: there exists the minimum of the intersection of two elements of is again an element of , and for all such that We prove that the set is a perfect numerical semigroup with...