25455 P. Garcia-Sanchez: Numerical semigroups - a minicourse. Internet, 17p.

25460 Ivan Martino: Signal functions on semigroups. Tesi LM Catania ca. 2010, 48p.

19599 J. Rosales/P. Garcia-Sanchez: Every numerical semigroup is one
half of a symmetric numerical semigroup. Proc. AMS ... (2007), 3p.
A numerical semigroup is a submonoid $S$ of $(\NN,+)$ such that
$\NN\setminus S$ is finite.

J. Rosales/P. Garcia-Sanchez: Numerical semigroups. Springer 2009, 180p. Eur 82.