title: `alldifferent` method in MiniZinc
body: <p>The following is the constraint I tried to implement in MiniZinc</p>
  
  <p><code>constraint forall (t in trucks)
  (all_different(c in customers where sequence[t,c] !=0) (sequence[t,c]));
  </code></p>
  
  <p>that is, I want every row element to be different for the <code>sequence</code> matrix when the <code>sequence</code> value doesn't equal to 0.</p>
  
  <p>and got the error </p>
  
  <p><code>MiniZinc: type error: no function or predicate with this signature found: all_different(array[int] of var opt int)'</code>.</p>
  
  <p>As indicated by some other threads I've added <code>include "alldifferent.mzn";</code> command, still showing that error.</p>
  
  <p>This is part of assignment, sorry for not able to push all my code here, please let me know if there is any extra information needed.</p>