# free algebra and indexed letters

I try to work with a Combinatorial Free Module with basis a set of Words over an alphabet of indexed letters (y1,y2,...). For example, I define

from sage.combinat.free_module import CombinatorialFreeModule as CFM Mots=Words(['y1','y2','y3','y4','y5','y6','y7','y8']) Module=CFM(QQ,Mots)

But I have some problems with the letters. For example :

mot=Word('y1') sage: mot word: y1 sage: mot in Mots False

Is there a way to cure this problem ?