Expressions involving Psi are combined as follows

where Q is a rational function, P a univariate polynomial and m and n are rationals.

This is done by applying the following recurrence and reflection formulae.

You can enter the command combine/Psi using either the 1-D or 2-D calling sequence. For example, combine(Psi(x) + Psi(1+x), Psi) is equivalent to .