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.
x1=tlist('x',1,2);
x2=tlist('x',2,3);
deff('x=%xmx(x1,x2)','x=list(''x'',x1(2)*x2(2),x2(3)*x2(3))');
x1*x2