Constraining a variable array in MiniZinc to contain all the elements of another constant set/array?

Question

I have an array of constant integers below-

array[1..7] of int: diff_check = 1..7 ;

I want to ensure that another variable array - array[int] of var int: differences; will contain all of the elements of the diff_check array, atleast once.

How do i go about doing this?

TIA