GCD of two polynomials with Euclide algorithm: gcd

### 2.25.7 GCD of two polynomials with Euclide algorithm: `gcd`

`gcd` denotes the gcd (greatest common divisor) of two polynomials (or of a list of polynomials or of a sequence of polynomials) (see also 2.6.2 for GCD of integers).

Examples
Input :

`gcd(x```^```2+2*x+1,x```^```2-1)`

Output :

`x+1`

Input :

`gcd(x```^```2-2*x+1,x```^```3-1,x```^```2-1,x```^```2+x-2)`

or

`gcd([x```^```2-2*x+1,x```^```3-1,x```^```2-1,x```^```2+x-2])`

Output :

`x-1`

For polynomials with modular coefficients, input e.g. :

`gcd((x```^```2+2*x+1) mod 5,(x```^```2-1) mod 5)`

Output :

`x % 5`

Note that :

`gcd(x```^```2+2*x+1,x```^```2-1) mod 5`

will output :

`1`

since the mod operation is done after the GCD is computed in ℤ[X].