Numerator and denominator : f2nd fxnd

f2nd (or fxnd) takes as argument a rational fraction and returns the liste of the numerator and the denominator of an irreducible representant of this fraction (see also 1.8.5).
Input :

f2nd((x^2-1)/(x-1))

Output :

[x+1,1]

Input :

f2nd((x^2+2*x+1)/(x^2-1))

Output :

[x+1,x-1]