Fix soundness bug in reduction of integer div/mod (#3766)

This was introduced 7 years ago in https://github.com/CVC4/CVC4/commit/9098391fe334d829ec4101f190b8f1fa21c30752.

This impacted any case of integer div/mod of the form `(mod c t)` or `(div c t)` where c is a constant and `t` is not.

Fixes #3765.

Also improves `--dump=t-lemmas` trace to result in smt-lib compatible output, which was required for debugging this.

5 files changed, 40 insertions, 3 deletions

diff --git a/src/theory/arith/theory_arith_private.cpp b/src/theory/arith/theory_arith_private.cpp
index 76d8dbc01..0ddded6bf 100644
--- a/src/theory/arith/theory_arith_private.cpp
+++ b/src/theory/arith/theory_arith_private.cpp
@@ -1603,7 +1603,7 @@ Node TheoryArithPrivate::axiomIteForTotalIntDivision(Node int_div_like){
   Polynomial rp = Polynomial::parsePolynomial(r);
   Polynomial qp = Polynomial::parsePolynomial(q);
 
-  Node abs_d = (n.isConstant()) ?
+  Node abs_d = (d.isConstant()) ?
     d.getHead().getConstant().abs().getNode() : mkIntSkolem("abs");
 
   Node eq = Comparison::mkComparison(EQUAL, n, d * qp + rp).getNode();
diff --git a/src/theory/theory_engine.cpp b/src/theory/theory_engine.cpp
index 7549bd973..b43e55364 100644
--- a/src/theory/theory_engine.cpp
+++ b/src/theory/theory_engine.cpp
@@ -1854,11 +1854,11 @@ theory::LemmaStatus TheoryEngine::lemma(TNode node,
 
   if(Dump.isOn("t-lemmas")) {
     Node n = node;
-    if (negated) {
+    if (!negated) {
       n = node.negate();
     }
     Dump("t-lemmas") << CommentCommand("theory lemma: expect valid")
-                     << QueryCommand(n.toExpr());
+                     << CheckSatCommand(n.toExpr());
   }
 
   // Share with other portfolio threads
diff --git a/test/regress/CMakeLists.txt b/test/regress/CMakeLists.txt
index 42c145762..1437baae1 100644
--- a/test/regress/CMakeLists.txt
+++ b/test/regress/CMakeLists.txt
@@ -1446,6 +1446,8 @@ set(regress_1_tests
   regress1/quantifiers/issue3628.smt2
   regress1/quantifiers/issue3664.smt2
   regress1/quantifiers/issue3724-quant.smt2
+  regress1/quantifiers/issue3765.smt2
+  regress1/quantifiers/issue3765-quant-dd.smt2
   regress1/quantifiers/issue993.smt2
   regress1/quantifiers/javafe.ast.StmtVec.009.smt2
   regress1/quantifiers/lra-vts-inf.smt2
diff --git a/test/regress/regress1/quantifiers/issue3765-quant-dd.smt2 b/test/regress/regress1/quantifiers/issue3765-quant-dd.smt2
new file mode 100644
index 000000000..624e5ddfa
--- /dev/null
+++ b/test/regress/regress1/quantifiers/issue3765-quant-dd.smt2
@@ -0,0 +1,18 @@
+; COMMAND-LINE: --finite-model-find --no-check-models
+; EXPECT: sat
+
+(set-logic ALL)
+
+(declare-sort U 0)
+(declare-fun g (U) Int)
+(declare-sort V 0)
+(declare-fun f (V) Int)
+(assert (and 
+(forall ((?i U)) (not (forall ((?z V)) (not (= (f ?z) (div (- 1) (g ?i))))) ))
+))
+
+(declare-fun k () U)
+(assert (= (g k) 22))
+
+
+(check-sat)
diff --git a/test/regress/regress1/quantifiers/issue3765.smt2 b/test/regress/regress1/quantifiers/issue3765.smt2
new file mode 100644
index 000000000..97e106365
--- /dev/null
+++ b/test/regress/regress1/quantifiers/issue3765.smt2
@@ -0,0 +1,17 @@
+; COMMAND-LINE: --fmf-fun --no-check-models

+; EXPECT: sat

+

+(set-info :smt-lib-version 2.5)

+(set-option :produce-models true)

+(set-logic ALL)

+(define-funs-rec (

+(f11((va9 Int))Int)

+(f3((v1f Int))Int)

+)

+( (f3 (ite (= 0 va9) (- 1) (div (- 1) va9)))

+ (- (ite (= 0 v1f) 0 (mod 0 v1f))) 

+))

+(declare-fun v18d() Int)

+(assert (= 0 (f11 v18d)))

+(assert (= 22 v18d))

+(check-sat)