Common denominator : comDenom

comDenom takes as argument a sum of rational fractions.
comDenom rewrite the sum as a unique rational fraction. The denominator of this rational fraction is the common denominator of the rational fractions given as argument.
Input :

comDenom(x-1/(x-1)-1/(x^2-1))

Output :

(x^3+-2*x-2)/(x^2-1)