# Non-homogenous Ideals In Unital Associative Free Algebras

Hi all,

I want to define a two sided ideal I=[x*y*x*y-x*y] in an unital associative free algebra K.<x,y>. But, the error I have faced to is the following:

ArithmaticError: Can only subtract the elements of the same degree.

Is there any way to define such an ideal in sage.

Thanks