Some syntax sugar
1 in [1,2,3]
.contains() is the best method for lists, but for maps you will need to use .containsKey() or .containsValue()
[a:1,b:2,c:3].containsValue(3)[a:1,b:2,c:3].containsKey('a')
For lists, use contains:
contains
[1,2,3].contains(1) == true