6.41.2 Testing if a value is in a list or a set: membercontains
The member and contains commands determine whether
or not an object is in a list; the difference between them is the
order of the arguments (required for compatibility reasons).
member takes two arguments:
c, a value.
L, a list or a set.
member(c,L) returns 0 if c is not an element of
L and otherwise returns n if c is in L and its first
position has index n−1.
0 if c is not in L.
Examples.
Input:
member(2,[0,1,2,3,4,2])
Output:
3
Input:
member(2,%{0,1,2,3,4,2%})
Output:
3
contains takes two arguments:
L, a list or a set.
c, a value.
contains(L,c) returns 0 if c is not an element of
L and otherwise returns n if c is in L and its first
position has index n−1.
0 if c is not in L.
