Determinacy Checker  
 Determinacy Checker: 
! warning: predicate user:(::-)/2 is discontiguous.
!          Some nondeterminism may have been missed.
!          Add (or move) the directive
!              :- discontiguous user:(::-)/2.
!          near the top of this file.
* Non-determinate: user:(::-)/2 (clause 1)
*     Indexing cannot distinguish this from clause 2.
* Non-determinate: user:(::-)/2 (clause 2)
*     Indexing cannot distinguish this from clause 3.