Frobenius restricted varieties in numerical semigroups
  The common behaviour of many families of numerical semigroups led up to defining, firstly, the Frobenius varieties and, secondly, the (Frobenius) pseudo-varieties. However, some interesting families are still out of these definitions. To overcome this situation, here we introduce the concept of restricted Frobenius variety (or R-variety). We will generalize most of the results for varieties and pseudo-varieties to R-varieties. In particular, we will study the tree structure that arise within them. 
Aureliano M. Robles-P\'erez and Jos\'e Carlos Rosales
math.GR