# How can you define a function that finds the Greatest Common Divisor (Gcd) two polynomials for every field?

Hi, as the title says I`m trying to define a function that finds the gcd of two polynomial without using the pre-established function gcd. I've tried everything I thought it would work:

First, I tried to use the Euclidan Algorithm, for that you need to divide the polynomials. Knowing so, I tried to find the degrees of the different polynomials to divide in consequence of the degrees (which gave me error). Then I tried it without the degree part and it didn't work at all since % couldn't be used as a divisor of polynomials.

```
def GCD(field, f, g):
R.<x> = PolynomialRing(field, 'x')
x.parent()
a = f.degree()
b = g.degree()
if a>b:
while g != 0:
r = g
g = f%g
else:
while f != 0:
r = g
f = g%f
return r
```

Shortly after I tried to factor both of the polynomial and make the función return the part that repeated. But I rapidly saw my hopes decay when I realized I have not a single clue in how to do so (even though I've done some research I couldn't find the answer).

```
def mcd(field, f, g):
R.<x> = PolynomialRing(field)
a = f.factor()
b = g.factor()
```

And this was the last code I wrote before asking for some enlightening:

```
def MCD(Field,PolynomialA, PolinomialB):
R.<x> = PolynomialRing(Field, 'x')
a = PolynomialA
b = PolynomialB
c = 1
while c != 0:
c = a%b
a = b
b = c
return a
```