Function: dilog
Section: transcendental
C-Name: dilog
Prototype: Gp
Help: dilog(x): dilogarithm of x.
Doc: principal branch of the dilogarithm of $x$,
 i.e.~analytic continuation of the power series
 $\text{Li}_{2}(x)=\sum_{n\ge1}x^{n}/n^{2}$.
