Small ints are not supported any longer; all integers (including constant literals, the result of the cardinality operator #, etc.) are always treated as sets of integers, i.e. Int.
Alloy built-in operators plus (+) and minus (-) are always treated as relational union and relational difference respectively.
For arithmetic operations, the users should always use the functions provided in util/integer.als. For example, what could be written previously as a+b and a-b must now be written a.plus[b] and a.minus[b] respectively.