Construction and Composition of Rooted Trees via Descent Functions
  We propose a novel approach for studying rooted trees by using functions that we will call descent functions. We provide a construction method for rooted trees that allows to study their properties through the use of descent functions. Moreover, in this way, we are able to compose rooted trees with each other. Such a new composition of rooted trees is a very powerful tool applied in this paper in order to obtain important results as the creation of new rational and Pythagorean trees. 
Marco Abrate, Stefano Barbero, Umberto Cerruti, Nadir Murru
math.NT math.CO