From e08e124790a0c4304599ef7b65eaceadcff11fd2 Mon Sep 17 00:00:00 2001
From: Jakob Rath <git@jakobrath.eu>
Date: Wed, 28 Sep 2022 10:57:40 +0200
Subject: [PATCH] Expand always-false check

---
 src/math/polysat/solver.cpp         |  1 +
 src/math/polysat/ule_constraint.cpp | 13 +++++++++----
 src/math/polysat/ule_constraint.h   |  2 +-
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/math/polysat/solver.cpp b/src/math/polysat/solver.cpp
index b975d83d7..85ccd7f26 100644
--- a/src/math/polysat/solver.cpp
+++ b/src/math/polysat/solver.cpp
@@ -196,6 +196,7 @@ namespace polysat {
             break;
         case l_undef:
             if (c.is_always_false()) {
+                LOG("Always false: " << c);
                 // asserted an always-false constraint
                 set_conflict_at_base_level();
                 return;
diff --git a/src/math/polysat/ule_constraint.cpp b/src/math/polysat/ule_constraint.cpp
index 389ff5ca1..d12af572b 100644
--- a/src/math/polysat/ule_constraint.cpp
+++ b/src/math/polysat/ule_constraint.cpp
@@ -134,17 +134,22 @@ namespace polysat {
         s.m_viable.intersect(p, q, sc);
     }
 
-    bool ule_constraint::is_always_false(bool is_positive, pdd const& lhs, pdd const& rhs) const {
-        // TODO: other conditions (e.g. when forbidden interval would be full)
+    bool ule_constraint::is_always_false(bool is_positive, pdd const& lhs, pdd const& rhs) {
         if (is_positive) {
+            // lhs <= rhs
             if (rhs.is_zero())
-                return lhs.is_never_zero();
+                return lhs.is_never_zero();  // p <= 0 implies p == 0
             return lhs.is_val() && rhs.is_val() && lhs.val() > rhs.val();
         }
         else {
+            // lhs > rhs
             if (lhs.is_zero())
                 return true;  // 0 > ... is always false
-            return (lhs.is_val() && rhs.is_val() && lhs.val() <= rhs.val()) || (lhs == rhs);
+            if (lhs == rhs)
+                return true;  // p > p
+            if (lhs.is_one() && rhs.is_never_zero())
+                return true;  // 1 > p implies p == 0
+            return lhs.is_val() && rhs.is_val() && lhs.val() <= rhs.val();
         }
     }
 
diff --git a/src/math/polysat/ule_constraint.h b/src/math/polysat/ule_constraint.h
index 990c468a6..87d74859d 100644
--- a/src/math/polysat/ule_constraint.h
+++ b/src/math/polysat/ule_constraint.h
@@ -34,7 +34,7 @@ namespace polysat {
         pdd const& rhs() const { return m_rhs; }
         std::ostream& display(std::ostream& out, lbool status) const override;
         std::ostream& display(std::ostream& out) const override;
-        bool is_always_false(bool is_positive, pdd const& lhs, pdd const& rhs) const;
+        static bool is_always_false(bool is_positive, pdd const& lhs, pdd const& rhs);
         bool is_always_false(bool is_positive) const override;
         bool is_currently_false(solver& s, bool is_positive) const override;
         bool is_currently_true(solver& s, bool is_positive) const override;