### 2.6.4 GCD of a list of integers : `lgcd`

`lgcd` has a list of integers (or of a list of polynomials)
as argument.

`lgcd` returns the `gcd` of all integers of the list (or
the `gcd` of all polynomials of the list).

Input :

`lgcd([18,15,21,36])`

Output :

`3`

**Remark**

`lgcd` does not accept two lists (even if they have the same size)
as arguments.