### 5.40.24 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 occurrence 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