Alloy analyser - only natural numbers - no integer set

Question

Is there a way to declare the natural numbers as in Int in Alloy?

Currently I have util/integer and if I run run 6 Int I get:

integers={-32, -31, -30, -29, -28, -27, -26, -25, -24, -23, -22, -21, -20, -19, -18, -17, -16, -15, -14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31}

what I want is util/naturalsand 3 Natural resulting in: naturals={0, 1, 2, 3, 4, 5, 6, 7, 8,...}

and not: natural/Natural={natural/Natural$0, natural/Natural$1, natural/Natural$2...}

Answer 1

If you want your numbers to be displayed so, without any signature name, you're IMHO pretty bound to use Int.

What you could do is thus to use a LET expression to define Natural as being the set of integer >=0.

I'd do it like this in Alloy 4.2

let Natural = {i : Int | i>=0}


sig A{
 a: Natural
}

run {} for 4 Int 

You should pay attention to enable "prevent overflow" in the Settings to be sure Natural doesn't contain negative number.