The recent COSY-11 collaboration measurement of the two-proton correlation function in the pp -> ppeta reaction, reported at this meeting [1], arouse some interest in a simple theoretical description of the correlation function. In these notes we pre
sent a pedagogical introduction to the practical methods that can be used for calculating the correlation function.
Based on the high statistics data from the pp -> ppX reaction measured by the COSY-11 collaboration [1] we have derived a two-proton correlation function for the production of the ppeta and pp+pions systems. The measured correlation function normaliz
ed to the value simulated for a point-like source was compared with a theoretical prediction in order to estimate the size of the reaction volume.