percent — (%) special character
Some predefined variables names begin with %, such as
%i (for sqrt(-1)), %inf (for Infinity), %pi (for 3.14...),
%T (for the boolean constant "true"),...
In addition, functions whose names begin with % are special :
they are used for primitives and operators overloading (see overloading).
For example the function %rmr performs the multiplication (m)
operation x*y for x and y rational matrices (r).
The coding conventions are given by the readme file in
directory SCIDIR/macros/percent.