From: notoria <notoria@users.noreply.github.com>
Date: Sun, 25 May 2025 11:37:28 +0000 (+0200)
Subject: Strengthened `(mod)/2` in CLP(Z)
X-Git-Tag: v0.10.0~43^2~2
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=37ac5bb3c1bcb4e7d973c9074cebf3536c2bb6de;p=scryer-prolog.git

Strengthened `(mod)/2` in CLP(Z)

?- Z = 8, X = 9, #Z #= #X mod #Y.
   Z = 8, X = 9, clpz:(Y in 9..sup), clpz:(9 mod#Y#=8). % unexpected
Expected: false
---

diff --git a/src/lib/clpz.pl b/src/lib/clpz.pl
index b14546bc..9daad75c 100644
--- a/src/lib/clpz.pl
+++ b/src/lib/clpz.pl
@@ -5088,11 +5088,21 @@ run_propagator(pmod(X,Y,Z), MState) -->
         ;   nonvar(Z), nonvar(X) ->
             (   Z > 0 ->
                 (   X < 0 -> true
-                ;   X >= Z
+                ;   X >= Z,
+                    % due to X = Z+Y*_ and Y > Z
+                    (   X-Z > 0 ->
+                        X-Z > Z
+                    ;   true
+                    )
                 )
             ;   Z < 0 ->
                 (   X > 0 -> true
-                ;   X =< Z
+                ;   X =< Z,
+                    % due to X = Z+Y*_ and Y < Z
+                    (   X-Z < 0 ->
+                        X-Z < Z
+                    ;   true
+                    )
                 )
             ;   Z =:= 0 % Multiple solutions so do nothing special.
             ),