From 4c799c144a2f7554b449dc3a0ad6432e4a348c3f Mon Sep 17 00:00:00 2001
From: Nikolaj Bjorner <nbjorner@microsoft.com>
Date: Fri, 22 Feb 2019 11:14:20 +0100
Subject: [PATCH] fix gc to not remove ternary clauses that are on assignment
 trail. This addresses issue with drat proofs that don't pass drat-trim due to
 deletion during gc, but use in conflicts

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
---
 src/sat/sat_clause.cpp        |   2 +-
 src/sat/sat_drat.cpp          | 113 +++++++++++++++++++++++++---------
 src/sat/sat_drat.h            |   4 ++
 src/sat/sat_elim_eqs.cpp      |   2 +-
 src/sat/sat_probing.cpp       |   3 +
 src/sat/sat_simplifier.cpp    |  24 ++++----
 src/sat/sat_simplifier.h      |   2 +-
 src/sat/sat_solver.cpp        |  88 ++++++++++++++++++++++----
 src/sat/sat_solver.h          |  23 +++----
 src/sat/sat_watched.cpp       |  10 ++-
 src/sat/tactic/sat_tactic.cpp |   1 +
 11 files changed, 201 insertions(+), 71 deletions(-)

diff --git a/src/sat/sat_clause.cpp b/src/sat/sat_clause.cpp
index d27820e71..03ae55092 100644
--- a/src/sat/sat_clause.cpp
+++ b/src/sat/sat_clause.cpp
@@ -38,7 +38,6 @@ namespace sat {
         memcpy(m_lits, lits, sizeof(literal) * sz);
         mark_strengthened();
         SASSERT(check_approx());
-        SASSERT(sz > 1);
     }
 
     var_approx_set clause::approx(unsigned num, literal const * lits) {
@@ -83,6 +82,7 @@ namespace sat {
         i++;
         for (; i < m_size; i++)
             m_lits[i-1] = m_lits[i];
+        m_lits[m_size-1] = l;
         m_size--;
         mark_strengthened();
     }
diff --git a/src/sat/sat_drat.cpp b/src/sat/sat_drat.cpp
index ac05b50f1..de65aca92 100644
--- a/src/sat/sat_drat.cpp
+++ b/src/sat/sat_drat.cpp
@@ -49,10 +49,13 @@ namespace sat {
         dealloc(m_bout);
         for (unsigned i = 0; i < m_proof.size(); ++i) {
             clause* c = m_proof[i];
-            if (c && (c->size() == 2 || m_status[i] == status::deleted || m_status[i] == status::external)) {
-                s.dealloc_clause(c);
+            if (c) {
+                m_alloc.del_clause(c);
             }
         }
+        m_proof.reset();
+        m_out = nullptr;
+        m_bout = nullptr;
     }
 
     void drat::updt_config() {
@@ -75,7 +78,7 @@ namespace sat {
         if (st == status::asserted || st == status::external) {
             return;
         }
-
+        
         char buffer[10000];
         char digits[20];     // enough for storing unsigned
         char* lastd = digits + sizeof(digits);
@@ -166,6 +169,9 @@ namespace sat {
     }
 
     void drat::append(literal l, status st) {
+        TRACE("sat_drat", tout << st << " " << l << "\n";);
+
+        declare(l);
         IF_VERBOSE(20, trace(verbose_stream(), 1, &l, st););
         if (st == status::learned) {
             verify(1, &l);
@@ -177,13 +183,15 @@ namespace sat {
             assign_propagate(l);
         }
 
-        clause* c = s.alloc_clause(1, &l, st == status::learned);
-        m_proof.push_back(c);
-        m_status.push_back(st);
+        m_units.push_back(l);
     }
 
     void drat::append(literal l1, literal l2, status st) {
+        TRACE("sat_drat", tout << st << " " << l1 << " " << l2 << "\n";);
+        declare(l1); 
+        declare(l2);
         literal lits[2] = { l1, l2 };
+        
         IF_VERBOSE(20, trace(verbose_stream(), 2, lits, st););
         if (st == status::deleted) {
             // noop
@@ -193,7 +201,7 @@ namespace sat {
             if (st == status::learned) {
                 verify(2, lits);
             }
-            clause* c = s.alloc_clause(2, lits, st == status::learned);
+            clause* c = m_alloc.mk_clause(2, lits, st == status::learned);
             m_proof.push_back(c);
             m_status.push_back(st);
             if (!m_check_unsat) return;
@@ -214,14 +222,37 @@ namespace sat {
         }
     }
 
+#if 0
+    // debugging code
+    bool drat::is_clause(clause& c, literal l1, literal l2, literal l3, drat::status st1, drat::status st2) {
+        //if (st1 != st2) return false;
+        if (c.size() != 3) return false;
+        if (l1 == c[0]) {
+            if (l2 == c[1] && l3 == c[2]) return true;
+            if (l2 == c[2] && l3 == c[1]) return true;
+        }
+        if (l2 == c[0]) {
+            if (l1 == c[1] && l3 == c[2]) return true;
+            if (l1 == c[2] && l3 == c[1]) return true;
+        }
+        if (l3 == c[0]) {
+            if (l1 == c[1] && l2 == c[2]) return true;
+            if (l1 == c[2] && l2 == c[1]) return true;
+        }
+        return false;
+    }
+#endif
+
     void drat::append(clause& c, status st) {
+        TRACE("sat_drat", tout << st << " " << c << "\n";);
+        for (literal lit : c) declare(lit);
         unsigned n = c.size();
         IF_VERBOSE(20, trace(verbose_stream(), n, c.begin(), st););
 
         if (st == status::learned) {
             verify(c);
         }
-
+           
         m_status.push_back(st);
         m_proof.push_back(&c); 
         if (st == status::deleted) {
@@ -274,6 +305,7 @@ namespace sat {
     }
 
     void drat::declare(literal l) {
+        if (!m_check) return;
         unsigned n = static_cast<unsigned>(l.var());
         while (m_assignment.size() <= n) {
             m_assignment.push_back(l_undef);
@@ -379,7 +411,7 @@ namespace sat {
                     case l_undef: num_undef++; break;
                     }
                 }
-                CTRACE("sat", num_true == 0 && num_undef == 1, display(tout););
+                CTRACE("sat_drat", num_true == 0 && num_undef == 1, display(tout););
                 SASSERT(num_true != 0 || num_undef != 1);
             }
         }
@@ -423,7 +455,7 @@ namespace sat {
             exit(0);
             UNREACHABLE();
             //display(std::cout);
-            TRACE("sat", 
+            TRACE("sat_drat", 
                   tout << literal_vector(n, c) << "\n";
                   display(tout); 
                   s.display(tout););
@@ -431,16 +463,41 @@ namespace sat {
         }
     }
 
+    bool drat::contains(literal c, justification const& j) {
+        if (!m_check_sat) {
+            return true;
+        }
+        switch (j.get_kind()) {
+        case justification::NONE:
+            return m_units.contains(c);
+        case justification::BINARY:
+            return contains(c, j.get_literal());
+        case justification::TERNARY:
+            return contains(c, j.get_literal1(), j.get_literal2());
+        case justification::CLAUSE: 
+            return contains(s.get_clause(j));
+        default:
+            return true;
+        }
+    }
+
     bool drat::contains(unsigned n, literal const* lits) {
         if (!m_check) return true;
+        unsigned num_add = 0;
+        unsigned num_del = 0;
         for (unsigned i = m_proof.size(); i-- > 0; ) {
             clause& c = *m_proof[i];
             status st = m_status[i];
             if (match(n, lits, c)) {
-                return st != status::deleted;
+                if (st == status::deleted) {
+                    num_del++;
+                } 
+                else {
+                    num_add++;
+                }
             }
         }
-        return false;
+        return num_add > num_del;
     }
 
     bool drat::match(unsigned n, literal const* lits, clause const& c) const {
@@ -454,7 +511,9 @@ namespace sat {
                         break;
                     }
                 }
-                if (!found) return false;
+                if (!found) {
+                    return false;
+                }
             }
             return true;
         }
@@ -512,7 +571,7 @@ namespace sat {
     void drat::assign(literal l) {
         lbool new_value = l.sign() ? l_false : l_true;
         lbool old_value = value(l);
-//        TRACE("sat", tout << "assign " << l << " := " << new_value << " from " << old_value << "\n";);
+//        TRACE("sat_drat", tout << "assign " << l << " := " << new_value << " from " << old_value << "\n";);
         switch (old_value) {
         case l_false:
             m_inconsistent = true;
@@ -544,7 +603,7 @@ namespace sat {
             watched_clause& wc = m_watched_clauses[idx];
             clause& c = *wc.m_clause;
 
-            //TRACE("sat", tout << "Propagate " << l << " " << c << " watch: " << wc.m_l1 << " " << wc.m_l2 << "\n";);
+            //TRACE("sat_drat", tout << "Propagate " << l << " " << c << " watch: " << wc.m_l1 << " " << wc.m_l2 << "\n";);
             if (wc.m_l1 == ~l) {
                 std::swap(wc.m_l1, wc.m_l2);
             }
@@ -596,17 +655,12 @@ namespace sat {
         }
     }
     void drat::add(literal l, bool learned) {
-        TRACE("sat", tout << "add: " << l << " " << (learned?"l":"t") << "\n";);
-        declare(l);
         status st = get_status(learned);
         if (m_out) dump(1, &l, st);
         if (m_bout) bdump(1, &l, st);
         if (m_check) append(l, st);
     }
     void drat::add(literal l1, literal l2, bool learned) {
-        TRACE("sat", tout << "add: " << l1 << " " << l2 << " " << (learned?"l":"t") << "\n";);
-        declare(l1);
-        declare(l2);
         literal ls[2] = {l1, l2};
         status st = get_status(learned);
         if (m_out) dump(2, ls, st);
@@ -614,12 +668,13 @@ namespace sat {
         if (m_check) append(l1, l2, st);
     }
     void drat::add(clause& c, bool learned) {
-        TRACE("sat", tout << "add: " << c << "\n";);
-        for (unsigned i = 0; i < c.size(); ++i) declare(c[i]);
         status st = get_status(learned);
         if (m_out) dump(c.size(), c.begin(), st);
         if (m_bout) bdump(c.size(), c.begin(), st);
-        if (m_check_unsat) append(c, get_status(learned));
+        if (m_check) {
+            clause* cl = m_alloc.mk_clause(c.size(), c.begin(), learned);
+            append(*cl, get_status(learned));
+        }
     }
     void drat::add(literal_vector const& lits, svector<premise> const& premises) {
         if (m_check) {
@@ -627,7 +682,7 @@ namespace sat {
             case 0: add(); break;
             case 1: append(lits[0], status::external); break;
             default: {
-                clause* c = s.alloc_clause(lits.size(), lits.c_ptr(), true);
+                clause* c = m_alloc.mk_clause(lits.size(), lits.c_ptr(), true);
                 append(*c, status::external);
                 break;
             }
@@ -635,16 +690,16 @@ namespace sat {
         }                        
     }
     void drat::add(literal_vector const& c) {
-        for (unsigned i = 0; i < c.size(); ++i) declare(c[i]);
         if (m_out) dump(c.size(), c.begin(), status::learned);
         if (m_bout) bdump(c.size(), c.begin(), status::learned);
         if (m_check) {
+            for (literal lit : c) declare(lit);
             switch (c.size()) {
             case 0: add(); break;
             case 1: append(c[0], status::learned); break;
             default: {
                 verify(c.size(), c.begin());
-                clause* cl = s.alloc_clause(c.size(), c.c_ptr(), true);
+                clause* cl = m_alloc.mk_clause(c.size(), c.c_ptr(), true);
                 append(*cl, status::external);                
                 break;
             }
@@ -657,8 +712,10 @@ namespace sat {
         if (m_bout) bdump(1, &l, status::deleted);
         if (m_check_unsat) append(l, status::deleted);
     }
+
     void drat::del(literal l1, literal l2) {
         literal ls[2] = {l1, l2};
+        SASSERT(!(l1 == literal(13923, false) && l2 == literal(14020, true)));
         if (m_out) dump(2, ls, status::deleted);
         if (m_bout) bdump(2, ls, status::deleted);
         if (m_check) append(l1, l2, status::deleted);
@@ -677,11 +734,11 @@ namespace sat {
         }
 #endif
 
-        TRACE("sat", tout << "del: " << c << "\n";);
+        //SASSERT(!(c.size() == 2 && c[0] == literal(13923, false) && c[1] == literal(14020, true)));
         if (m_out) dump(c.size(), c.begin(), status::deleted);
         if (m_bout) bdump(c.size(), c.begin(), status::deleted);
         if (m_check) {
-            clause* c1 = s.alloc_clause(c.size(), c.begin(), c.is_learned()); 
+            clause* c1 = m_alloc.mk_clause(c.size(), c.begin(), c.is_learned()); 
             append(*c1, status::deleted);
         }
     }
diff --git a/src/sat/sat_drat.h b/src/sat/sat_drat.h
index 35e5a0655..7224da063 100644
--- a/src/sat/sat_drat.h
+++ b/src/sat/sat_drat.h
@@ -45,6 +45,7 @@ namespace sat {
         svector<watched_clause>   m_watched_clauses;
         typedef svector<unsigned> watch;
         solver& s;
+        clause_allocator        m_alloc;
         std::ostream*           m_out;
         std::ostream*           m_bout;
         ptr_vector<clause>      m_proof;
@@ -61,6 +62,8 @@ namespace sat {
         void append(literal l1, literal l2, status st);
         void append(clause& c, status st);
 
+        bool is_clause(clause& c, literal l1, literal l2, literal l3, status st1, status st2);
+
         friend std::ostream& operator<<(std::ostream & out, status st);
         status get_status(bool learned) const;
 
@@ -104,6 +107,7 @@ namespace sat {
         bool contains(unsigned n, literal const* c);
         bool contains(literal l1, literal l2) { literal lits[2] = {l1, l2}; return contains(2, lits); }
         bool contains(literal l1, literal l2, literal l3) { literal lits[3] = {l1, l2, l3}; return contains(3, lits); }
+        bool contains(literal c, justification const& j);
 
         void check_model(model const& m);
     };
diff --git a/src/sat/sat_elim_eqs.cpp b/src/sat/sat_elim_eqs.cpp
index bc69c1f5d..7e19bf520 100644
--- a/src/sat/sat_elim_eqs.cpp
+++ b/src/sat/sat_elim_eqs.cpp
@@ -207,7 +207,7 @@ namespace sat {
                     c.update_approx();
                 }
                 if (m_solver.m_config.m_drat) {
-                    m_solver.m_drat.add(c, true); 
+                    m_solver.m_drat.add(c, true);
                     drat_delete_clause();
                 }
 
diff --git a/src/sat/sat_probing.cpp b/src/sat/sat_probing.cpp
index 5689112d4..e12e78560 100644
--- a/src/sat/sat_probing.cpp
+++ b/src/sat/sat_probing.cpp
@@ -52,6 +52,9 @@ namespace sat {
         unsigned tr_sz = s.m_trail.size();
         for (unsigned i = old_tr_sz; i < tr_sz; i++) {
             entry.m_lits.push_back(s.m_trail[i]);
+            if (s.m_config.m_drat) {
+                s.m_drat.add(~l, s.m_trail[i], true);
+            }
         }
     }
 
diff --git a/src/sat/sat_simplifier.cpp b/src/sat/sat_simplifier.cpp
index 58dab0ff5..86094d7a3 100644
--- a/src/sat/sat_simplifier.cpp
+++ b/src/sat/sat_simplifier.cpp
@@ -124,9 +124,9 @@ namespace sat {
         }
     }
 
-    inline void simplifier::remove_clause(clause & c) {
+    inline void simplifier::remove_clause(clause & c, bool is_unique) {
         if (!c.was_removed()) {
-            if (s.m_config.m_drat) {
+            if (s.m_config.m_drat && is_unique) {
                 s.m_drat.del(c);
             }
             for (literal l : c) {
@@ -477,7 +477,7 @@ namespace sat {
                     s.set_learned(c1, false);
                 }
                 TRACE("subsumption", tout << c1 << " subsumed " << c2 << "\n";);
-                remove_clause(c2);
+                remove_clause(c2, false);
                 m_num_subsumed++;
             }
             else if (!c2.was_removed()) {
@@ -577,7 +577,7 @@ namespace sat {
             if (c1.is_learned() && !c2.is_learned())
                 s.set_learned(c1, false);
             TRACE("subsumption", tout << c1 << " subsumed " << c2 << "\n";);
-            remove_clause(c2);
+            remove_clause(c2, false);
             m_num_subsumed++;
         }
     }
@@ -662,7 +662,7 @@ namespace sat {
             for (auto it = cs.mk_iterator(); !it.at_end(); ) {
                 clause & c = it.curr();
                 it.next();
-                remove_clause(c);
+                remove_clause(c, true);
             }
             cs.reset();            
         }
@@ -674,10 +674,12 @@ namespace sat {
         m_num_elim_lits++;
         insert_elim_todo(l.var());
         if (s.m_config.m_drat && c.contains(l)) {
-            m_dummy.set(c.size(), c.begin(), c.is_learned());
+            unsigned sz = c.size();
             c.elim(l);
             s.m_drat.add(c, true); 
-            s.m_drat.del(*m_dummy.get());
+            c.restore(sz);
+            s.m_drat.del(c);
+            c.shrink(sz-1);
         }
         else {
             c.elim(l);
@@ -690,7 +692,7 @@ namespace sat {
         if (cleanup_clause(c)) {
             // clause was satisfied
             TRACE("elim_lit", tout << "clause was satisfied\n";);
-            remove_clause(c);
+            remove_clause(c, true);
             return;
         }
         unsigned sz = c.size();
@@ -710,7 +712,7 @@ namespace sat {
             c.restore(sz0);
             s.mk_bin_clause(c[0], c[1], c.is_learned());
             m_sub_bin_todo.push_back(bin_clause(c[0], c[1], c.is_learned()));            
-            remove_clause(c);
+            remove_clause(c, sz0 != sz);
             break;
         default:
             if (s.m_config.m_drat && sz0 != sz) {
@@ -888,7 +890,7 @@ namespace sat {
             if (s.m_trail.size() > m_last_sub_trail_sz) {
                 unsigned sz0 = c.size();
                 if (cleanup_clause(c)) {
-                    remove_clause(c);
+                    remove_clause(c, true);
                     continue;
                 }
                 unsigned sz = c.size();
@@ -906,7 +908,7 @@ namespace sat {
                     s.mk_bin_clause(c[0], c[1], c.is_learned());
                     m_sub_bin_todo.push_back(bin_clause(c[0], c[1], c.is_learned()));
                     c.restore(sz0);
-                    remove_clause(c);
+                    remove_clause(c, sz != sz0);
                     continue;
                 default:
                     if (s.m_config.m_drat && sz != sz0) {
diff --git a/src/sat/sat_simplifier.h b/src/sat/sat_simplifier.h
index 2aa2b4252..895ebdcb5 100644
--- a/src/sat/sat_simplifier.h
+++ b/src/sat/sat_simplifier.h
@@ -133,7 +133,7 @@ namespace sat {
 
         void register_clauses(clause_vector & cs);
 
-        void remove_clause(clause & c);
+        void remove_clause(clause & c, bool is_unique);
         void set_learned(clause & c);
         void set_learned(literal l1, literal l2);
 
diff --git a/src/sat/sat_solver.cpp b/src/sat/sat_solver.cpp
index 3deb6fc17..4a0397cee 100644
--- a/src/sat/sat_solver.cpp
+++ b/src/sat/sat_solver.cpp
@@ -33,19 +33,22 @@ Revision History:
 
 namespace sat {
 
+    static unsigned s_lemma_count = 0;
+    static bool     s_verify_contains = false;
+
     solver::solver(params_ref const & p, reslimit& l):
         solver_core(l),
         m_checkpoint_enabled(true),
         m_config(p),
         m_par(nullptr),
         m_cls_allocator_idx(false),
+        m_drat(*this),
         m_cleaner(*this),
         m_simplifier(*this, p),
         m_scc(*this, p),
         m_asymm_branch(*this, p),
         m_probing(*this, p),
         m_mus(*this),
-        m_drat(*this),
         m_inconsistent(false),
         m_searching(false),
         m_num_frozen(0),
@@ -382,6 +385,9 @@ namespace sat {
             if (!learned && !at_search_lvl()) 
                 m_clauses_to_reinit.push_back(clause_wrapper(l1, l2));
         }
+        if (l1 == literal(29327, false) && l2 == literal(29328, false)) {
+            std::cout << s_lemma_count << "\n";            
+        }
         m_stats.m_mk_bin_clause++;
         get_wlist(~l1).push_back(watched(l2, learned));
         get_wlist(~l2).push_back(watched(l1, learned));
@@ -413,8 +419,6 @@ namespace sat {
         clause * r = alloc_clause(3, lits, learned);
         bool reinit = attach_ter_clause(*r);
         if (reinit && !learned) push_reinit_stack(*r);
-        if (m_config.m_drat) m_drat.add(*r, learned);
-
         if (learned)
             m_learned.push_back(r);
         else
@@ -424,6 +428,9 @@ namespace sat {
 
     bool solver::attach_ter_clause(clause & c) {
         bool reinit = false;
+        if (m_config.m_drat) m_drat.add(c, c.is_learned());
+        TRACE("sat", tout << c << "\n";);
+        SASSERT(!c.was_removed());
         m_watches[(~c[0]).index()].push_back(watched(c[1], c[2]));
         m_watches[(~c[1]).index()].push_back(watched(c[0], c[2]));
         m_watches[(~c[2]).index()].push_back(watched(c[0], c[1]));
@@ -459,8 +466,9 @@ namespace sat {
         else {
             m_clauses.push_back(r);
         }
-        if (m_config.m_drat) 
+        if (m_config.m_drat) {
             m_drat.add(*r, learned);
+        }
         return r;
     }
 
@@ -2163,6 +2171,36 @@ namespace sat {
         IF_VERBOSE(SAT_VB_LVL, verbose_stream() << "(sat-gc :strategy " << st_name << " :deleted " << (sz - new_sz) << ")\n";);
     }
 
+    bool solver::can_delete3(literal l1, literal l2, literal l3) const {                                                           
+        if (value(l1) == l_true && 
+            value(l2) == l_false && 
+            value(l3) == l_false) {
+            justification const& j = m_justification[l1.var()];
+            if (j.is_ternary_clause()) {
+                watched w1(l2, l3);
+                watched w2(j.get_literal1(), j.get_literal2());
+                return w1 != w2;
+            }
+        }
+        return true;
+    }
+
+    bool solver::can_delete(clause const & c) const {
+        if (c.on_reinit_stack())
+            return false;
+        if (c.size() == 3) {
+            return
+                can_delete3(c[0],c[1],c[2]) &&
+                can_delete3(c[1],c[0],c[2]) &&
+                can_delete3(c[2],c[0],c[1]);
+        }
+        literal l0 = c[0];
+        if (value(l0) != l_true)
+            return true;
+        justification const & jst = m_justification[l0.var()];
+        return !jst.is_clause() || cls_allocator().get_clause(jst.get_clause_offset()) != &c;
+    }
+
     /**
        \brief Use gc based on dynamic psm. Clauses are initially frozen.
     */
@@ -2381,6 +2419,21 @@ namespace sat {
             }
         }
 
+        s_lemma_count++;
+
+        if (s_lemma_count == 51802) {
+            disable_trace("sat");
+            disable_trace("sat_conflict");
+            s_verify_contains = false;
+        }
+
+
+        if (s_lemma_count == 51801) {
+            enable_trace("sat");
+            enable_trace("sat_conflict");
+            s_verify_contains = true;
+        }
+
         m_lemma.reset();
 
         unsigned idx = skip_literals_above_conflict_level();
@@ -2401,6 +2454,9 @@ namespace sat {
         do {
             TRACE("sat_conflict_detail", tout << "processing consequent: " << consequent << "\n";
                   tout << "num_marks: " << num_marks << ", js: " << js << "\n";);
+
+            // VERIFY(!s_verify_contains || !m_config.m_drat || m_drat.contains(consequent, js));
+
             switch (js.get_kind()) {
             case justification::NONE:
                 break;
@@ -2455,6 +2511,8 @@ namespace sat {
             idx--;
             num_marks--;
             reset_mark(c_var);
+
+            TRACE("sat", display_justification(tout << consequent << " ", js) << "\n";);            
         }
         while (num_marks > 0);
 
@@ -2467,12 +2525,13 @@ namespace sat {
         TRACE("sat_lemma", tout << "new lemma size: " << m_lemma.size() << "\n" << m_lemma << "\n";);
 
         unsigned new_scope_lvl       = 0;
+        bool sub_min = false, res_min = false;
         if (!m_lemma.empty()) {
             if (m_config.m_minimize_lemmas) {
-                minimize_lemma();
+                res_min = minimize_lemma();
                 reset_lemma_var_marks();
                 if (m_config.m_dyn_sub_res)
-                    dyn_sub_res();
+                    sub_min = dyn_sub_res();
                 TRACE("sat_lemma", tout << "new lemma (after minimization) size: " << m_lemma.size() << "\n" << m_lemma << "\n";);
             }
             else
@@ -2492,12 +2551,12 @@ namespace sat {
         m_slow_glue_avg.update(glue);
         pop_reinit(m_scope_lvl - new_scope_lvl);
         TRACE("sat_conflict_detail", tout << glue << " " << new_scope_lvl << "\n";);
-        // unsound: m_asymm_branch.minimize(m_scc, m_lemma);
         clause * lemma = mk_clause_core(m_lemma.size(), m_lemma.c_ptr(), true);
         if (lemma) {
             lemma->set_glue(glue);
             if (m_par) m_par->share_clause(*this, *lemma);
         }
+
         TRACE("sat_conflict_detail", tout << new_scope_lvl << "\n";);
         decay_activity();
         updt_phase_counters();
@@ -2844,7 +2903,7 @@ namespace sat {
             if (m_lvl_set.may_contain(var_lvl)) {
                 mark(var);
                 m_unmark.push_back(var);
-                m_lemma_min_stack.push_back(var);
+                m_lemma_min_stack.push_back(antecedent);
             }
             else {
                 return false;
@@ -2862,11 +2921,12 @@ namespace sat {
     */
     bool solver::implied_by_marked(literal lit) {
         m_lemma_min_stack.reset();  // avoid recursive function
-        m_lemma_min_stack.push_back(lit.var());
+        m_lemma_min_stack.push_back(lit);
         unsigned old_size = m_unmark.size();
 
         while (!m_lemma_min_stack.empty()) {
-            bool_var var       = m_lemma_min_stack.back();
+            lit = m_lemma_min_stack.back();
+            bool_var var = lit.var();
             m_lemma_min_stack.pop_back();
             justification const& js   = m_justification[var];
             switch(js.get_kind()) {
@@ -2928,6 +2988,8 @@ namespace sat {
                 UNREACHABLE();
                 break;
             }
+            TRACE("sat_conflict", 
+                  display_justification(tout << var << " ",js) << "\n";);
         }
         return true;
     }
@@ -2958,7 +3020,7 @@ namespace sat {
        literals that are implied by other literals in m_lemma and/or literals
        assigned at level 0.
     */
-    void solver::minimize_lemma() {
+    bool solver::minimize_lemma() {
         SASSERT(!m_lemma.empty());
         SASSERT(m_unmark.empty());
         updt_lemma_lvl_set();
@@ -2982,6 +3044,7 @@ namespace sat {
         reset_unmark(0);
         m_lemma.shrink(j);
         m_stats.m_minimized_lits += sz - j;
+        return j < sz;
     }
 
     /**
@@ -3055,7 +3118,7 @@ namespace sat {
        \brief Apply dynamic subsumption resolution to new lemma.
        Only binary and ternary clauses are used.
     */
-    void solver::dyn_sub_res() {
+    bool solver::dyn_sub_res() {
         unsigned sz = m_lemma.size();
         for (unsigned i = 0; i < sz; i++) {
             mark_lit(m_lemma[i]);
@@ -3168,6 +3231,7 @@ namespace sat {
 
         SASSERT(j >= 1);
         m_lemma.shrink(j);
+        return j < sz;
     }
 
 
diff --git a/src/sat/sat_solver.h b/src/sat/sat_solver.h
index c000ccb79..47e226cc4 100644
--- a/src/sat/sat_solver.h
+++ b/src/sat/sat_solver.h
@@ -85,9 +85,10 @@ namespace sat {
         stats                   m_stats;
         scoped_ptr<extension>   m_ext;
         parallel*               m_par;
-        random_gen              m_rand;
+        drat                    m_drat;          // DRAT for generating proofs
         clause_allocator        m_cls_allocator[2];
         bool                    m_cls_allocator_idx;
+        random_gen              m_rand;
         cleaner                 m_cleaner;
         model                   m_model;        
         model_converter         m_mc;
@@ -97,7 +98,6 @@ namespace sat {
         asymm_branch            m_asymm_branch;
         probing                 m_probing;
         mus                     m_mus;           // MUS for minimal core extraction
-        drat                    m_drat;          // DRAT for generating proofs
         bool                    m_inconsistent;
         bool                    m_searching;
         // A conflict is usually a single justification. That is, a justification
@@ -461,17 +461,8 @@ namespace sat {
         void gc_dyn_psm();
         bool activate_frozen_clause(clause & c);
         unsigned psm(clause const & c) const;
-        bool can_delete(clause const & c) const {
-            if (c.on_reinit_stack())
-                return false;
-            if (c.size() == 3)
-                return true; // not needed to justify anything.
-            literal l0 = c[0];
-            if (value(l0) != l_true)
-                return true;
-            justification const & jst = m_justification[l0.var()];
-            return !jst.is_clause() || cls_allocator().get_clause(jst.get_clause_offset()) != &c;
-        }
+        bool can_delete(clause const & c) const;
+        bool can_delete3(literal l1, literal l2, literal l3) const;
 
         clause& get_clause(watch_list::iterator it) const {
             SASSERT(it->get_kind() == watched::CLAUSE);
@@ -522,14 +513,14 @@ namespace sat {
         typedef approx_set_tpl<unsigned, u2u, unsigned> level_approx_set;
         bool_var_vector   m_unmark;
         level_approx_set  m_lvl_set;
-        bool_var_vector   m_lemma_min_stack;
+        literal_vector    m_lemma_min_stack;
         bool process_antecedent_for_minimization(literal antecedent);
         bool implied_by_marked(literal lit);
         void reset_unmark(unsigned old_size);
         void updt_lemma_lvl_set();
-        void minimize_lemma();
         void reset_lemma_var_marks();
-        void dyn_sub_res();
+        bool minimize_lemma();
+        bool dyn_sub_res();
 
         // -----------------------
         //
diff --git a/src/sat/sat_watched.cpp b/src/sat/sat_watched.cpp
index 966bd8325..8811a4e74 100644
--- a/src/sat/sat_watched.cpp
+++ b/src/sat/sat_watched.cpp
@@ -86,7 +86,15 @@ namespace sat {
             }    
         }
         wlist.set_end(it2);
-        //VERIFY(found);
+#if 0
+        VERIFY(found);
+        for (watched const& w2 : wlist) {
+            if (w2 == w) {
+                std::cout << l1 << " " << l2 << "\n";
+            }
+            //VERIFY(w2 != w);
+        }
+#endif
     }
 
     void conflict_cleanup(watch_list::iterator it, watch_list::iterator it2, watch_list& wlist) {
diff --git a/src/sat/tactic/sat_tactic.cpp b/src/sat/tactic/sat_tactic.cpp
index 2739932e6..b2137795b 100644
--- a/src/sat/tactic/sat_tactic.cpp
+++ b/src/sat/tactic/sat_tactic.cpp
@@ -200,6 +200,7 @@ public:
             throw tactic_exception(ex.msg());
         }
         catch (z3_exception& ex) {
+            (void)ex;
             TRACE("sat", tout << ex.msg() << "\n";);            
             throw;
         }