On gluing a surface of genus $g$ from two and three polygons
  In this paper the number of ways to glue together several polygons into a surface of genus $g$ has been investigated. We've given an elementary proof on the formula for the generating function $\mathbf{C}_g^{[2]}(z)$ of the number of gluings surface of genus $g$ from two polygons (see also [4]). Moreover, we've proven a similar formula for gluings surface of genus $g$ from three polygons. As a corollary, we've proven a direct formula for the number of gluings torus from three polygons. 
Alexei Pastor
math.CO