diff --git a/src/math/lp/lar_solver.h b/src/math/lp/lar_solver.h
index 622e12b80..588befcd7 100644
--- a/src/math/lp/lar_solver.h
+++ b/src/math/lp/lar_solver.h
@@ -404,6 +404,8 @@ public:
     void update_x_and_inf_costs_for_column_with_changed_bounds(unsigned j);
 
     
+    unsigned num_changed_bounds() const { return m_rows_with_changed_bounds.size(); }
+
     void detect_rows_with_changed_bounds_for_column(unsigned j);
     
     void detect_rows_with_changed_bounds();
diff --git a/src/sat/sat_aig_cuts.cpp b/src/sat/sat_aig_cuts.cpp
index 55060f2ea..069a418a0 100644
--- a/src/sat/sat_aig_cuts.cpp
+++ b/src/sat/sat_aig_cuts.cpp
@@ -275,6 +275,18 @@ namespace sat {
         SASSERT(!m_aig[v].empty());
     }
 
+    void aig_cuts::add_cut(bool_var v, uint64_t lut, bool_var_vector const& args) {
+        reserve(v);
+        for (bool_var w : args) reserve(w); 
+        // optional: reshuffle lut and sort variables.
+        cut c;
+        for (bool_var w : args) VERIFY(c.add(w));
+        c.set_table(lut);
+        // add-don't care?
+        insert_cut(v, c, m_cuts[v]);
+    }
+
+
     void aig_cuts::set_root(bool_var v, literal r) {
         IF_VERBOSE(10, verbose_stream() << "set-root " << v << " -> " << r << "\n");
         m_roots.push_back(std::make_pair(v, r));
diff --git a/src/sat/sat_aig_cuts.h b/src/sat/sat_aig_cuts.h
index 2c6f28bb6..530367bce 100644
--- a/src/sat/sat_aig_cuts.h
+++ b/src/sat/sat_aig_cuts.h
@@ -158,6 +158,7 @@ namespace sat {
         aig_cuts();
         void add_var(unsigned v);
         void add_node(literal head, bool_op op, unsigned sz, literal const* args);
+        void add_cut(bool_var v, uint64_t lut, bool_var_vector const& args);
         void set_root(bool_var v, literal r);
 
         void set_on_clause_add(on_clause_t& on_clause_add);
diff --git a/src/sat/sat_aig_simplifier.cpp b/src/sat/sat_aig_simplifier.cpp
index fcae49d9e..c7d53a280 100644
--- a/src/sat/sat_aig_simplifier.cpp
+++ b/src/sat/sat_aig_simplifier.cpp
@@ -230,8 +230,9 @@ namespace sat {
 
 #if 0
         std::function<void(uint64_t, bool_var_vector const&, bool_var)> on_lut = 
-            [&,this](uint64_t l, bool_var_vector const& vars, bool_var v) {
+            [&,this](uint64_t lut, bool_var_vector const& vars, bool_var v) {
             m_stats.m_xluts++;
+            m_aig_cuts.add_cut(v, lut, vars);
         };
         lut_finder lf(s);
         lf.set(on_lut);
diff --git a/src/smt/smt_consequences.cpp b/src/smt/smt_consequences.cpp
index 3a25e5f52..b71561c5a 100644
--- a/src/smt/smt_consequences.cpp
+++ b/src/smt/smt_consequences.cpp
@@ -513,7 +513,7 @@ namespace smt {
         if (m_asserted_formulas.inconsistent() || inconsistent()) {
             return l_false;
         }
-        scoped_mk_model smk(*this);
+        reset_model();
         init_search();
         flet<bool> l(m_searching, true);
         unsigned level = m_scope_lvl;
diff --git a/src/smt/smt_context.cpp b/src/smt/smt_context.cpp
index b58d77f81..267274cdd 100644
--- a/src/smt/smt_context.cpp
+++ b/src/smt/smt_context.cpp
@@ -3343,8 +3343,10 @@ namespace smt {
             r = l_undef;
         }
         if (r == l_true && gparams::get_value("model_validate") == "true") {
+            model_ref mdl;
+            get_model(mdl);
             for (theory* t : m_theory_set) {
-                t->validate_model(*m_model);
+                t->validate_model(*mdl);
             }
 #if 0
             for (literal lit : m_assigned_literals) {
@@ -3560,7 +3562,7 @@ namespace smt {
             return l_false;
         }
         timeit tt(get_verbosity_level() >= 100, "smt.stats");
-        scoped_mk_model smk(*this);
+        reset_model();
         SASSERT(at_search_level());
         TRACE("search", display(tout); display_enodes_lbls(tout););
         TRACE("search_detail", m_asserted_formulas.display(tout););
@@ -3594,35 +3596,34 @@ namespace smt {
     }
 
     bool context::restart(lbool& status, unsigned curr_lvl) {
+        SASSERT(status != l_true || !inconsistent());
+
+        reset_model();
 
         if (m_last_search_failure != OK) {
-            if (status != l_false) {
-                // build candidate model before returning
-                mk_proto_model(status);
-                // status = l_undef;
-            }
             return false;
         }
-
         if (status == l_false) {
             return false;
         }
-        if (status == l_true) {
-            SASSERT(!inconsistent());
-            mk_proto_model(l_true);
+        if (status == l_true && !m_qmanager->has_quantifiers()) {
+            return false;
+        }
+        if (status == l_true && m_qmanager->has_quantifiers()) {
             // possible outcomes   DONE l_true, DONE l_undef, CONTINUE
+            mk_proto_model();
             quantifier_manager::check_model_result cmr = m_qmanager->check_model(m_proto_model.get(), m_model_generator->get_root2value());
-            if (cmr == quantifier_manager::SAT) {
-                // done
-                status = l_true;
+            switch (cmr) {
+            case quantifier_manager::SAT:
                 return false;
-            }
-            if (cmr == quantifier_manager::UNKNOWN) {
+            case quantifier_manager::UNKNOWN:
                 IF_VERBOSE(2, verbose_stream() << "(smt.giveup quantifiers)\n";);
                 // giving up
                 m_last_search_failure = QUANTIFIERS;
                 status = l_undef;
                 return false;
+            default:
+                break;
             }
         }
         inc_limits();
@@ -3807,7 +3808,7 @@ namespace smt {
 
         
         if (m_fparams.m_model_on_final_check) {
-            mk_proto_model(l_undef);
+            mk_proto_model();
             model_pp(std::cout, *m_proto_model);
             std::cout << "END_OF_MODEL\n";
             std::cout.flush();
@@ -4395,15 +4396,16 @@ namespace smt {
         }
         TRACE("opt", tout << (refinalize?"refinalize":"no-op") << " " << fcs << "\n";);
         if (fcs == FC_DONE) {
-            mk_proto_model(l_true);
-            m_model = m_proto_model->mk_model();
-            add_rec_funs_to_model();
+            reset_model();
+            model_ref mdl;
+            get_model(mdl);
         }
 
         return fcs == FC_DONE;
     }
 
-    void context::mk_proto_model(lbool r) {
+    void context::mk_proto_model() {
+        if (m_model || m_proto_model) return;
         TRACE("get_model",
               display(tout);
               display_normalized_enodes(tout);
@@ -4412,9 +4414,10 @@ namespace smt {
               );
         failure fl = get_last_search_failure();
         if (fl == MEMOUT || fl == CANCELED || fl == NUM_CONFLICTS || fl == RESOURCE_LIMIT) {
-            TRACE("get_model", tout << "last search failure: " << fl << "\n";);
-        }
-        else if (m_fparams.m_model || m_fparams.m_model_on_final_check || m_qmanager->model_based()) {
+            TRACE("get_model", tout << "last search failure: " << fl << "\n";);   
+        }     
+        else if (m_fparams.m_model || m_fparams.m_model_on_final_check || 
+                 (m_qmanager->has_quantifiers() && m_qmanager->model_based())) {
             m_model_generator->reset();
             m_proto_model = m_model_generator->mk_model();
             m_qmanager->adjust_model(m_proto_model.get());
@@ -4427,8 +4430,7 @@ namespace smt {
         }
     }
 
-    proof * context::get_proof() {
-        
+    proof * context::get_proof() {        
         if (!m_unsat_proof) {
             m_unsat_proof = m_clause_proof.get_proof();
         }
@@ -4436,11 +4438,22 @@ namespace smt {
         return m_unsat_proof;
     }
 
-    void context::get_model(model_ref & m) const {
+    void context::get_model(model_ref & m) {
         if (inconsistent())
             m = nullptr;
-        else
-            m = const_cast<model*>(m_model.get());
+        else {
+            mk_proto_model();
+            if (!m_model && m_proto_model) {
+                m_model = m_proto_model->mk_model();
+                try {
+                    add_rec_funs_to_model();
+                }
+                catch (...) {
+                    // no op
+                }                
+            }
+            m = m_model.get();
+        }
     }
 
     void context::get_levels(ptr_vector<expr> const& vars, unsigned_vector& depth) {
@@ -4459,10 +4472,6 @@ namespace smt {
         return result;
     }
 
-    void context::get_proto_model(proto_model_ref & m) const {
-        m = const_cast<proto_model*>(m_proto_model.get());
-    }
-
     failure context::get_last_search_failure() const {
         return m_last_search_failure;
     }
diff --git a/src/smt/smt_context.h b/src/smt/smt_context.h
index f25ff52e2..e45363132 100644
--- a/src/smt/smt_context.h
+++ b/src/smt/smt_context.h
@@ -215,27 +215,8 @@ namespace smt {
         proto_model_ref            m_proto_model;
         model_ref                  m_model;
         std::string                m_unknown;
-        void                       mk_proto_model(lbool r);
-        struct scoped_mk_model {
-            context & m_ctx;
-            scoped_mk_model(context & ctx):m_ctx(ctx) {
-                m_ctx.m_proto_model = nullptr;
-                m_ctx.m_model       = nullptr;
-            }
-            ~scoped_mk_model() {
-                if (m_ctx.m_proto_model.get() != nullptr) {
-                    m_ctx.m_model = m_ctx.m_proto_model->mk_model();
-                    try {
-                        m_ctx.add_rec_funs_to_model();
-                    }
-                    catch (...) {
-                        // no op
-                    }
-                    m_ctx.m_proto_model = nullptr; // proto_model is not needed anymore.
-                }
-            }
-        };
-
+        void                       mk_proto_model();
+        void                       reset_model() { m_model = nullptr; m_proto_model = nullptr; }
 
         // -----------------------------------
         //
@@ -1614,12 +1595,12 @@ namespace smt {
 
         expr_ref_vector get_trail();
 
-        void get_model(model_ref & m) const;
+        void get_model(model_ref & m);
+
+        void set_model(model* m) { m_model = m; }
 
         bool update_model(bool refinalize);
 
-        void get_proto_model(proto_model_ref & m) const;
-
         bool validate_model();
 
         unsigned get_num_asserted_formulas() const { return m_asserted_formulas.get_num_formulas(); }
diff --git a/src/smt/smt_kernel.cpp b/src/smt/smt_kernel.cpp
index 1d7280a48..bd25e2592 100644
--- a/src/smt/smt_kernel.cpp
+++ b/src/smt/smt_kernel.cpp
@@ -132,7 +132,7 @@ namespace smt {
             return m_kernel.find_mutexes(vars, mutexes);
         }
         
-        void get_model(model_ref & m) const {
+        void get_model(model_ref & m) {
             m_kernel.get_model(m);
         }
 
@@ -315,7 +315,7 @@ namespace smt {
         return m_imp->find_mutexes(vars, mutexes);
     }
 
-    void kernel::get_model(model_ref & m) const {
+    void kernel::get_model(model_ref & m) {
         m_imp->get_model(m);
     }
 
diff --git a/src/smt/smt_kernel.h b/src/smt/smt_kernel.h
index 2cf3f4e7b..e9223f827 100644
--- a/src/smt/smt_kernel.h
+++ b/src/smt/smt_kernel.h
@@ -153,7 +153,7 @@ namespace smt {
         /**
            \brief Return the model associated with the last check command.
         */
-        void get_model(model_ref & m) const;
+        void get_model(model_ref & m);
 
         /**
            \brief Return the proof of unsatisfiability associated with the last check command.
diff --git a/src/smt/smt_parallel.cpp b/src/smt/smt_parallel.cpp
index f19fafa37..5b32574c3 100644
--- a/src/smt/smt_parallel.cpp
+++ b/src/smt/smt_parallel.cpp
@@ -206,7 +206,7 @@ namespace smt {
         case l_true: 
             pctx.get_model(mdl);
             if (mdl) {
-                ctx.m_model = mdl->translate(tr);
+                ctx.set_model(mdl->translate(tr));
             }
             break;
         case l_false:
diff --git a/src/smt/smt_quantifier.cpp b/src/smt/smt_quantifier.cpp
index d0ca05ff9..b96229e57 100644
--- a/src/smt/smt_quantifier.cpp
+++ b/src/smt/smt_quantifier.cpp
@@ -165,6 +165,8 @@ namespace smt {
             m_plugin->add(q);
         }
 
+        bool has_quantifiers() const { return !m_quantifiers.empty(); }
+
         void display_stats(std::ostream & out, quantifier * q) {
             quantifier_stat * s     = get_stat(q);
             unsigned num_instances  = s->get_num_instances();
@@ -478,6 +480,10 @@ namespace smt {
         return m_imp->m_plugin->model_based();
     }
 
+    bool quantifier_manager::has_quantifiers() const {
+        return m_imp->has_quantifiers();
+    }
+
     bool quantifier_manager::mbqi_enabled(quantifier *q) const {
         return m_imp->m_plugin->mbqi_enabled(q);
     }
diff --git a/src/smt/smt_quantifier.h b/src/smt/smt_quantifier.h
index a25ada87e..ca8e4ceb5 100644
--- a/src/smt/smt_quantifier.h
+++ b/src/smt/smt_quantifier.h
@@ -79,6 +79,7 @@ namespace smt {
         };
 
         bool model_based() const;
+        bool has_quantifiers() const;
         bool mbqi_enabled(quantifier *q) const; // can mbqi instantiate this quantifier?
         void adjust_model(proto_model * m);
         check_model_result check_model(proto_model * m, obj_map<enode, app *> const & root2value);
diff --git a/src/smt/theory_lra.cpp b/src/smt/theory_lra.cpp
index d981a13f0..c39b8f3ce 100644
--- a/src/smt/theory_lra.cpp
+++ b/src/smt/theory_lra.cpp
@@ -1623,7 +1623,7 @@ public:
         svector<lpvar> vars;
         theory_var sz = static_cast<theory_var>(th.get_num_vars());
         for (theory_var v = 0; v < sz; ++v) {
-            if (can_be_used_in_random_update(v))
+            if (th.is_relevant_and_shared(get_enode(v))) 
                 vars.push_back(get_lpvar(v));
         }
         if (vars.empty()) {
@@ -2368,20 +2368,36 @@ public:
             
     }
 
-    void propagate_bounds_with_lp_solver() {
-        if (BP_NONE == propagation_mode()) {
-            return;
+    unsigned m_propagation_delay{1};
+    unsigned m_propagation_count{0};
+    
+    bool should_propagate() {
+        ++m_propagation_count;
+        return BP_NONE != propagation_mode() && (m_propagation_count >= m_propagation_delay);
+    }
+
+    void update_propagation_threshold(bool made_progress) {
+        m_propagation_count = 0;
+        if (made_progress) {
+            m_propagation_delay = std::max(1u, m_propagation_delay-1u);
         }
-        int num_of_p = lp().settings().stats().m_num_of_implied_bounds;
-        (void)num_of_p;
+        else {
+            m_propagation_delay += 2;
+        }
+    }
+
+    void propagate_bounds_with_lp_solver() {
+        if (!should_propagate()) 
+            return;
         local_bound_propagator bp(*this);
+        unsigned num_changed = lp().num_changed_bounds();
+
         lp().propagate_bounds_for_touched_rows(bp);
         if (m.canceled()) {
             return;
         }
-        int new_num_of_p = lp().settings().stats().m_num_of_implied_bounds;
-        (void)new_num_of_p;
-        CTRACE("arith", new_num_of_p > num_of_p, tout << "found " << new_num_of_p << " implied bounds\n";);
+        unsigned props = m_stats.m_bound_propagations1;
+
         if (is_infeasible()) {
             get_infeasibility_explanation_and_set_conflict();
         }
@@ -2390,28 +2406,26 @@ public:
                 propagate_lp_solver_bound(bp.m_ibounds[i]);
             }
         }
+        update_propagation_threshold(props < m_stats.m_bound_propagations1);
     }
 
     bool bound_is_interesting(unsigned vi, lp::lconstraint_kind kind, const rational & bval) const {
         theory_var v = lp().local_to_external(vi);
-        if (v == null_theory_var) 
+        if (v == null_theory_var) {
             return false;
-
+        }
         if (m_unassigned_bounds[v] == 0 || m_bounds.size() <= static_cast<unsigned>(v)) {
             return false;
         }
         for (lp_api::bound* b : m_bounds[v]) {
             if (ctx().get_assignment(b->get_bv()) == l_undef &&
-                null_literal != is_bound_implied(kind, bval, *b))
+                null_literal != is_bound_implied(kind, bval, *b)) {
                 return true;
+            }
         }
         return false;
     }
 
-    nla::solver* get_nla_solver() {        
-        return m_switcher.m_nla ? m_switcher.m_nla->get() : nullptr;
-    }
-
     struct local_bound_propagator: public lp::lp_bound_propagator {
         imp & m_imp;
         local_bound_propagator(imp& i) : lp_bound_propagator(*i.m_solver), m_imp(i) {}
@@ -2476,7 +2490,7 @@ public:
                   );
             DEBUG_CODE(
                 for (auto& lit : m_core) {
-                                          SASSERT(ctx().get_assignment(lit) == l_true);
+                    VERIFY(ctx().get_assignment(lit) == l_true);
                 });
             ++m_stats.m_bound_propagations1;
             assign(lit);
diff --git a/src/util/mpz.cpp b/src/util/mpz.cpp
index 4d93ea24d..6a7c531cc 100644
--- a/src/util/mpz.cpp
+++ b/src/util/mpz.cpp
@@ -1525,12 +1525,12 @@ void mpz_manager<SYNCH>::big_set(mpz & target, mpz const & source) {
 template<bool SYNCH>
 int mpz_manager<SYNCH>::big_compare(mpz const & a, mpz const & b) {
 #ifndef _MP_GMP
-    sign_cell ca(*this, a), cb(*this, b);
 
-    if (ca.sign() > 0) {
+    if (sign(a) > 0) {
         // a is positive
-        if (cb.sign() > 0) {
+        if (sign(b) > 0) {
             // a & b are positive
+            sign_cell ca(*this, a), cb(*this, b);
             return m_mpn_manager.compare(ca.cell()->m_digits, ca.cell()->m_size,
                                          cb.cell()->m_digits, cb.cell()->m_size);
         }
@@ -1541,12 +1541,13 @@ int mpz_manager<SYNCH>::big_compare(mpz const & a, mpz const & b) {
     }
     else {
         // a is negative
-        if (cb.sign() > 0) {
+        if (sign(b) > 0) {
             // b is positive
             return -1; // a < b
         }
         else {
             // a & b are negative
+            sign_cell ca(*this, a), cb(*this, b);
             return m_mpn_manager.compare(cb.cell()->m_digits, cb.cell()->m_size,
                                          ca.cell()->m_digits, ca.cell()->m_size);
         }