Maxima documentation about "facsum" writes:
" With no variable specification, for example facsum (expr), the result
returned is the same as that returned by ratsimp (expr). "
Let's try:
(%i1) expr: a*b*x^3+a*c*x^3;
(%o1) a*c*x^3+a*b*x^3
(%i2) ratsimp(expr);
(%o2) (a*c+a*b)*x^3
(%i3) facsum(expr);
(%o3) a*(c+b)*x^3
Hope this will be useful for documentation update. I think that the it would
be greatly improved by adding to each topic few meaningful examples, without
many words.
Mario M.