f2nd (or fxnd) takes as argument a rational fraction and
returns the list of the numerator and the denominator of the irreducible
representation of this fraction (see also 5.8.5).

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]