Test if a value is in a list : contains

contains takes as argument a list (or a set) L and a value c.
contains tests if c is an element of the list L.
contains returns 0 if c is not in L, or a strictly positive integer which is 1+the index of the first occurence of c in L.
Input :

contains([0,1,2,3,4,2],2)

Output :

3

Input :

contains(%{0,1,2,3,4,2%},2)

Output :

3