How to constrain a year field to 1-4?

Question

There is a set of college students:

sig Student {}

Each student has an attribute indicating what year he/she is in college (first year, second year, etc.):

sig Student {
    year: Int
}

The value of year must be 1, 2, 3, or 4. Here is one way to constrain the year field:

sig Student {
    year: Int
} {
 year in {i: Int | i=1 or i=2 or i=3 or i=4}
}

Is there a better (simpler, more intuitive) way to constrain year?

Answer 1

-- Enumerate
let YEARS = 1+2+3+4

-- or Range
let YEARS = { y : Int | y >= 1 and y <= 4 }

sig Student { year: Int } {
  year in YEARS
}

Or more concise

sig Student { year: YEARS }