Test if a value is in a list : member

### 2.37.23 Test if a value is in a list : `member`

`member` takes as argument a value `c` and a list (or a set) `L`.
`member` is a function that tests if `c` is an element of the list `L`.
`member` returns `0` if `c` is not in `L`, or a strictly positive integer which is 1 plus the index of the first occurence of `c` in `L`.
Note the order of the arguments (required for compatibility reasons)
Input :

`member(2,[0,1,2,3,4,2])`

Output :

`3`

Input :

`member(2,%{0,1,2,3,4,2%})`

Output :

`3`