Universidad de Valladolid, España
In his mathematical stage in Valladolid, Guillermo Cortiñas made great progress in obtaining results for the algebraic K-theory available for the topological K-theory. At the same time, in the same Department, by our joint work with Delgado and Gusein-Zade, we began to develop an algebraic notion of several variable Poincaré series, created before in 1998, which allows to read topology. Today, Poincaré series have algebraic and topological sides. We review the evolution of the Poincaré series over 25 years and present some current results.