diff --git a/contrib/cmake/src/opt/CMakeLists.txt b/contrib/cmake/src/opt/CMakeLists.txt
index b8d17ec89..05a62b6c2 100644
--- a/contrib/cmake/src/opt/CMakeLists.txt
+++ b/contrib/cmake/src/opt/CMakeLists.txt
@@ -9,6 +9,7 @@ z3_add_component(opt
     optsmt.cpp
     opt_solver.cpp
     pb_sls.cpp
+    sortmax.cpp
     wmax.cpp
   COMPONENT_DEPENDENCIES
     sat_solver
diff --git a/src/muz/pdr/pdr_context.cpp b/src/muz/pdr/pdr_context.cpp
index 6d3a57581..01a9a4416 100644
--- a/src/muz/pdr/pdr_context.cpp
+++ b/src/muz/pdr/pdr_context.cpp
@@ -584,6 +584,7 @@ namespace pdr {
         init_atom(pts, rule.get_head(), var_reprs, conj, UINT_MAX);
         for (unsigned i = 0; i < ut_size; ++i) {
             if (rule.is_neg_tail(i)) {
+                dealloc(&var_reprs);
                 throw default_exception("PDR does not support negated predicates in rule tails");
             }
             init_atom(pts, rule.get_tail(i), var_reprs, conj, i);
@@ -602,7 +603,13 @@ namespace pdr {
             var_subst(m, false)(tail[i].get(), var_reprs.size(), (expr*const*)var_reprs.c_ptr(), tmp);
             conj.push_back(tmp);
             TRACE("pdr", tout << mk_pp(tail[i].get(), m) << "\n" << mk_pp(tmp, m) << "\n";);
-            SASSERT(is_ground(tmp));
+            if (!is_ground(tmp)) {
+                std::stringstream msg;
+                msg << "PDR cannot solve non-ground tails: " << tmp;
+                IF_VERBOSE(0, verbose_stream() << msg.str() << "\n";);
+                dealloc(&var_reprs);
+                throw default_exception(msg.str());
+            }
         }
         expr_ref fml = pm.mk_and(conj);
         th_rewriter rw(m);
diff --git a/src/opt/maxres.cpp b/src/opt/maxres.cpp
index 016f1ee0e..7f9183d9a 100644
--- a/src/opt/maxres.cpp
+++ b/src/opt/maxres.cpp
@@ -162,7 +162,6 @@ public:
         if (m_asm2weight.find(e, weight)) {
             weight += w;
             m_asm2weight.insert(e, weight);
-            m_upper += w;
             return;
         }
         if (is_literal(e)) {
@@ -174,7 +173,6 @@ public:
             s().assert_expr(fml);
         }
         new_assumption(asum, w);
-        m_upper += w;
     }
 
     void new_assumption(expr* e, rational const& w) {
@@ -805,7 +803,6 @@ public:
     }
 
     lbool init_local() {
-        m_upper.reset();
         m_lower.reset();
         m_trail.reset();
         obj_map<expr, rational> new_soft;
diff --git a/src/opt/maxsmt.cpp b/src/opt/maxsmt.cpp
index 97ce28166..85b19e427 100644
--- a/src/opt/maxsmt.cpp
+++ b/src/opt/maxsmt.cpp
@@ -235,6 +235,9 @@ namespace opt {
         else if (maxsat_engine == symbol("wmax")) {
             m_msolver = mk_wmax(m_c, m_weights, m_soft_constraints);
         }
+        else if (maxsat_engine == symbol("sortmax")) {
+            m_msolver = mk_sortmax(m_c, m_weights, m_soft_constraints);
+        }
         else {
             warning_msg("solver %s is not recognized, using default 'maxres'", maxsat_engine.str().c_str());
             m_msolver = mk_maxres(m_c, m_index, m_weights, m_soft_constraints);
diff --git a/src/opt/sortmax.cpp b/src/opt/sortmax.cpp
new file mode 100644
index 000000000..6df827896
--- /dev/null
+++ b/src/opt/sortmax.cpp
@@ -0,0 +1,141 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    sortmax.cpp
+
+Abstract:
+
+    Theory based MaxSAT.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2016-11-18
+
+Notes:
+
+--*/
+#include "maxsmt.h"
+#include "uint_set.h"
+#include "ast_pp.h"
+#include "model_smt2_pp.h"
+#include "smt_theory.h"
+#include "smt_context.h"
+#include "opt_context.h"
+#include "sorting_network.h"
+#include "filter_model_converter.h"
+
+namespace opt {
+
+    class sortmax : public maxsmt_solver_base {
+    public:
+        typedef expr* literal;
+        typedef ptr_vector<expr> literal_vector;
+        psort_nw<sortmax> m_sort;
+        expr_ref_vector   m_trail;
+        func_decl_ref_vector m_fresh;
+        ref<filter_model_converter> m_filter;
+        sortmax(maxsat_context& c, weights_t& ws, expr_ref_vector const& soft): 
+            maxsmt_solver_base(c, ws, soft), m_sort(*this), m_trail(m), m_fresh(m) {}
+
+        virtual ~sortmax() {}
+
+        lbool operator()() {
+            obj_map<expr, rational> soft;            
+            if (!init()) {
+                return l_false;
+            }
+            lbool is_sat = find_mutexes(soft);
+            if (is_sat != l_true) {
+                return is_sat;
+            }
+            m_filter = alloc(filter_model_converter, m);
+            rational offset = m_lower;
+            m_upper = offset;
+            expr_ref_vector in(m);
+            expr_ref tmp(m);
+            ptr_vector<expr> out;
+            obj_map<expr, rational>::iterator it = soft.begin(), end = soft.end();
+            for (; it != end; ++it) {
+                unsigned n = it->m_value.get_unsigned();
+                while (n > 0) {
+                    in.push_back(it->m_key);
+                    --n;
+                }
+                m_upper += it->m_value;
+            }
+            m_sort.sorting(in.size(), in.c_ptr(), out);
+            unsigned first = 0;
+            while (l_true == is_sat && first < out.size() && m_lower < m_upper) {
+                trace_bounds("sortmax");
+                s().assert_expr(out[first]);
+                is_sat = s().check_sat(0, 0);
+                TRACE("opt", tout << is_sat << "\n"; s().display(tout); tout << "\n";);
+                if (m.canceled()) {
+                    is_sat = l_undef;
+                }
+                if (is_sat == l_true) {
+                    ++first;
+                    s().get_model(m_model);
+                    update_assignment();
+                    for (; first < out.size() && is_true(out[first]); ++first) { 
+                        s().assert_expr(out[first]);
+                    }
+                    TRACE("opt", model_smt2_pp(tout, m, *m_model.get(), 0););
+                    m_upper = m_lower + rational(out.size() - first);
+                    (*m_filter)(m_model);
+                }
+            }
+            if (is_sat == l_false) {
+                is_sat = l_true;
+                m_lower = m_upper;
+            }
+            TRACE("opt", tout << "min cost: " << m_upper << "\n";);
+            return is_sat;
+        }
+
+        void update_assignment() {
+            for (unsigned i = 0; i < m_soft.size(); ++i) {
+                m_assignment[i] = is_true(m_soft[i]);
+            }
+        }
+
+        bool is_true(expr* e) {
+            expr_ref tmp(m);
+            return m_model->eval(e, tmp) && m.is_true(tmp);
+        }
+
+        // definitions used for sorting network
+        literal mk_false() { return m.mk_false(); }
+        literal mk_true() { return m.mk_true(); }
+        literal mk_max(literal a, literal b) { return trail(m.mk_or(a, b)); }
+        literal mk_min(literal a, literal b) { return trail(m.mk_and(a, b)); }
+        literal mk_not(literal a) { if (m.is_not(a,a)) return a; return trail(m.mk_not(a)); }
+
+        std::ostream& pp(std::ostream& out, literal lit) {  return out << mk_pp(lit, m);  }
+        
+        literal trail(literal l) {
+            m_trail.push_back(l);
+            return l;
+        }
+        literal fresh() {
+            expr_ref fr(m.mk_fresh_const("sn", m.mk_bool_sort()), m);
+            func_decl* f = to_app(fr)->get_decl();
+            m_fresh.push_back(f);
+            m_filter->insert(f);
+            return trail(fr);
+        }
+        
+        void mk_clause(unsigned n, literal const* lits) {
+            s().assert_expr(mk_or(m, n, lits));
+        }        
+        
+    };
+    
+    
+    maxsmt_solver_base* mk_sortmax(maxsat_context& c, weights_t& ws, expr_ref_vector const& soft) {
+        return alloc(sortmax, c, ws, soft);
+    }
+
+}
diff --git a/src/opt/wmax.cpp b/src/opt/wmax.cpp
index d3ceb9a3b..7e0e796ca 100644
--- a/src/opt/wmax.cpp
+++ b/src/opt/wmax.cpp
@@ -51,7 +51,10 @@ namespace opt {
             obj_map<expr, rational>::iterator it = soft.begin(), end = soft.end();
             for (; it != end; ++it) {
                 wth().assert_weighted(it->m_key, it->m_value);
-                m_upper += it->m_value;
+                expr_ref tmp(m);
+                if (!m_model->eval(it->m_key, tmp) || !m.is_true(tmp)) {
+                    m_upper += it->m_value;
+                }
             }
             trace_bounds("wmax");
             while (l_true == is_sat && m_lower < m_upper) {
diff --git a/src/opt/wmax.h b/src/opt/wmax.h
index 094bb8644..3d9d206ad 100644
--- a/src/opt/wmax.h
+++ b/src/opt/wmax.h
@@ -25,5 +25,7 @@ Notes:
 namespace opt {
     maxsmt_solver_base* mk_wmax(maxsat_context& c, weights_t & ws, expr_ref_vector const& soft);
 
+    maxsmt_solver_base* mk_sortmax(maxsat_context& c, weights_t & ws, expr_ref_vector const& soft);
+
 }
 #endif
diff --git a/src/sat/sat_solver.cpp b/src/sat/sat_solver.cpp
index 7acfda822..9cf13afe4 100644
--- a/src/sat/sat_solver.cpp
+++ b/src/sat/sat_solver.cpp
@@ -21,6 +21,7 @@ Revision History:
 #include"luby.h"
 #include"trace.h"
 #include"sat_bceq.h"
+#include"max_cliques.h"
 
 // define to update glue during propagation
 #define UPDATE_GLUE
@@ -3062,74 +3063,44 @@ namespace sat {
     //
     // -----------------------
 
+    struct neg_literal {
+        unsigned negate(unsigned idx) {
+            return (~to_literal(idx)).index();
+        }
+    };
+
     lbool solver::find_mutexes(literal_vector const& lits, vector<literal_vector> & mutexes) {
-        literal_vector ps(lits);
+        max_cliques<neg_literal> mc;
         m_user_bin_clauses.reset();
         m_binary_clause_graph.reset();
         collect_bin_clauses(m_user_bin_clauses, true);
         collect_bin_clauses(m_user_bin_clauses, false);
+        hashtable<literal_pair, pair_hash<literal_hash, literal_hash>, default_eq<literal_pair> > seen_bc;
         for (unsigned i = 0; i < m_user_bin_clauses.size(); ++i) {
             literal l1 = m_user_bin_clauses[i].first;
             literal l2 = m_user_bin_clauses[i].second;
-            m_binary_clause_graph.reserve(l1.index() + 1);
-            m_binary_clause_graph.reserve(l2.index() + 1);
-            m_binary_clause_graph.reserve((~l1).index() + 1);
-            m_binary_clause_graph.reserve((~l2).index() + 1);
-            m_binary_clause_graph[l1.index()].push_back(l2);
-            m_binary_clause_graph[l2.index()].push_back(l1);
+            literal_pair p(l1, l2);
+            if (!seen_bc.contains(p)) {
+                seen_bc.insert(p);
+                mc.add_edge(l1.index(), l2.index());             
+            }
         }
+        vector<unsigned_vector> _mutexes;
+        unsigned_vector ps;
         for (unsigned i = 0; i < lits.size(); ++i) {
-            m_binary_clause_graph.reserve(lits[i].index() + 1);
-            m_binary_clause_graph.reserve((~lits[i]).index() + 1);
+            ps.push_back(lits[i].index());
         }
-        bool non_empty = true;
-        m_seen[0].reset();
-        while (non_empty) {
-            literal_vector mutex;
-            bool turn = false;
-            m_reachable[turn] = ps;
-            while (!m_reachable[turn].empty()) {
-                literal p = m_reachable[turn].pop();
-                if (m_seen[0].contains(p)) {
-                    continue;
-                }
-                m_reachable[turn].remove(p);
-                m_seen[0].insert(p);
-                mutex.push_back(p);
-                if (m_reachable[turn].empty()) {
-                    break;
-                }
-                m_reachable[!turn].reset();
-                get_reachable(p, m_reachable[turn], m_reachable[!turn]);
-                turn = !turn;
+        mc.cliques(ps, _mutexes);
+        for (unsigned i = 0; i < _mutexes.size(); ++i) {
+            literal_vector lits;
+            for (unsigned j = 0; j < _mutexes[i].size(); ++j) {
+                lits.push_back(to_literal(_mutexes[i][j]));
             }
-            if (mutex.size() > 1) {
-                mutexes.push_back(mutex);
-            }
-            non_empty = !mutex.empty();
+            mutexes.push_back(lits);
         }
         return l_true;
     }
 
-    void solver::get_reachable(literal p, literal_set const& goal, literal_set& reachable) {
-        m_seen[1].reset();
-        m_todo.reset();
-        m_todo.push_back(p);
-        while (!m_todo.empty()) {
-            p = m_todo.back();
-            m_todo.pop_back();
-            if (m_seen[1].contains(p)) {
-                continue;
-            }
-            m_seen[1].insert(p);
-            literal np = ~p;
-            if (goal.contains(np)) {
-                reachable.insert(np);
-            }
-            m_todo.append(m_binary_clause_graph[np.index()]);
-        }
-    }
-
     // -----------------------
     //
     // Consequence generation.
diff --git a/src/sat/sat_solver.h b/src/sat/sat_solver.h
index a44f07a23..bcd9a66d2 100644
--- a/src/sat/sat_solver.h
+++ b/src/sat/sat_solver.h
@@ -451,14 +451,9 @@ namespace sat {
 
         u_map<index_set>       m_antecedents;
         vector<literal_vector> m_binary_clause_graph;
-        literal_set            m_reachable[2];
-        literal_set            m_seen[2];
-        literal_vector         m_todo;
 
         void extract_assumptions(literal lit, index_set& s);
 
-        void get_reachable(literal p, literal_set const& goal, literal_set& reachable);
-
         lbool get_consequences(literal_vector const& assms, literal_vector const& lits, vector<literal_vector>& conseq);
 
         void delete_unfixed(literal_set& unfixed);
diff --git a/src/sat/sat_types.h b/src/sat/sat_types.h
index 509cc58ba..28d8d761a 100644
--- a/src/sat/sat_types.h
+++ b/src/sat/sat_types.h
@@ -96,6 +96,7 @@ namespace sat {
     };
 
     const literal null_literal;
+    struct literal_hash : obj_hash<literal> {};
 
     inline literal to_literal(unsigned x) { return literal(x); }
     inline bool operator<(literal const & l1, literal const & l2) { return l1.m_val < l2.m_val;  }
diff --git a/src/smt/params/qi_params.cpp b/src/smt/params/qi_params.cpp
index a341040ce..8182222e4 100644
--- a/src/smt/params/qi_params.cpp
+++ b/src/smt/params/qi_params.cpp
@@ -62,4 +62,4 @@ void qi_params::display(std::ostream & out) const {
     DISPLAY_PARAM(m_mbqi_trace);
     DISPLAY_PARAM(m_mbqi_force_template);
     DISPLAY_PARAM(m_mbqi_id);
-}
\ No newline at end of file
+}
diff --git a/src/smt/smt_consequences.cpp b/src/smt/smt_consequences.cpp
index 667411be5..e6edbf87e 100644
--- a/src/smt/smt_consequences.cpp
+++ b/src/smt/smt_consequences.cpp
@@ -20,6 +20,8 @@ Revision History:
 #include "ast_util.h"
 #include "datatype_decl_plugin.h"
 #include "model_pp.h"
+#include "max_cliques.h"
+#include "stopwatch.h"
 
 namespace smt {
 
@@ -367,67 +369,46 @@ namespace smt {
              << ")\n";
     }  
 
+    struct neg_literal {
+        unsigned negate(unsigned i) {
+            return (~to_literal(i)).index();
+        }
+    };
 
     lbool context::find_mutexes(expr_ref_vector const& vars, vector<expr_ref_vector>& mutexes) {
-        uint_set lits;
+        unsigned_vector ps;
+        max_cliques<neg_literal> mc;
+        expr_ref lit(m_manager);
         for (unsigned i = 0; i < vars.size(); ++i) {
             expr* n = vars[i];
             bool neg = m_manager.is_not(n, n);
             if (b_internalized(n)) {
-                lits.insert(literal(get_bool_var(n), neg).index());
+                ps.push_back(literal(get_bool_var(n), neg).index());
             }
         }
-        while (!lits.empty()) {
-            literal_vector mutex;
-            uint_set other(lits);
-            while (!other.empty()) {
-                uint_set conseq;
-                literal p = to_literal(*other.begin());
-                other.remove(p.index());
-                mutex.push_back(p);
-                if (other.empty()) {
-                    break;
+        for (unsigned i = 0; i < m_watches.size(); ++i) {
+            watch_list & w = m_watches[i];
+            for (literal const* it = w.begin_literals(), *end = w.end_literals(); it != end; ++it) {
+                unsigned idx1 = (~to_literal(i)).index();
+                unsigned idx2 = it->index();
+                if (idx1 < idx2) {
+                    mc.add_edge(idx1, idx2);
                 }
-                get_reachable(p, other, conseq);
-                other = conseq;
-            }
-            if (mutex.size() > 1) {
-                expr_ref_vector mux(m_manager);
-                for (unsigned i = 0; i < mutex.size(); ++i) {
-                    expr_ref e(m_manager);
-                    literal2expr(mutex[i], e);
-                    mux.push_back(e);
-                }
-                mutexes.push_back(mux);
-            }
-            for (unsigned i = 0; i < mutex.size(); ++i) {
-                lits.remove(mutex[i].index());
             }
         }
+        vector<unsigned_vector> _mutexes;
+        mc.cliques(ps, _mutexes);
+        for (unsigned i = 0; i < _mutexes.size(); ++i) {
+            expr_ref_vector lits(m_manager);
+            for (unsigned j = 0; j < _mutexes[i].size(); ++j) {
+                literal2expr(to_literal(_mutexes[i][j]), lit);
+                lits.push_back(lit);
+            }
+            mutexes.push_back(lits);
+        }        
         return l_true;
     }
 
-    void context::get_reachable(literal p, uint_set& goal, uint_set& reachable) {
-        uint_set seen;
-        literal_vector todo;
-        todo.push_back(p);
-        while (!todo.empty()) {
-            // std::cout << "todo: " << todo.size() << "\n";
-            p = todo.back();
-            todo.pop_back();
-            if (seen.contains(p.index())) {
-                continue;
-            }
-            seen.insert(p.index());
-            literal np = ~p;
-            if (goal.contains(np.index())) {
-                reachable.insert(np.index());
-            }
-            watch_list & w = m_watches[np.index()];
-            todo.append(static_cast<unsigned>(w.end_literals() - w.begin_literals()), w.begin_literals());
-        }
-    }
-
     //
     // Validate, in a slow pass, that the current consequences are correctly 
     // extracted.
diff --git a/src/smt/smt_context.h b/src/smt/smt_context.h
index 84459d272..21d628e1a 100644
--- a/src/smt/smt_context.h
+++ b/src/smt/smt_context.h
@@ -1367,11 +1367,6 @@ namespace smt {
         void validate_consequences(expr_ref_vector const& assumptions, expr_ref_vector const& vars, 
                                    expr_ref_vector const& conseq, expr_ref_vector const& unfixed);
 
-        /*
-          \brief Auxiliry function for mutex finding.
-         */
-
-        void get_reachable(literal p, uint_set& goal, uint_set& reached);
 
     public:
         context(ast_manager & m, smt_params & fp, params_ref const & p = params_ref());
diff --git a/src/smt/smt_model_checker.cpp b/src/smt/smt_model_checker.cpp
index c17211664..a7f415aad 100644
--- a/src/smt/smt_model_checker.cpp
+++ b/src/smt/smt_model_checker.cpp
@@ -194,6 +194,7 @@ namespace smt {
               }
               tout << "\n";);
         
+        max_generation = std::max(m_qm->get_generation(q), max_generation);
         add_instance(q, bindings, max_generation);
         return true;
     }
diff --git a/src/util/max_cliques.h b/src/util/max_cliques.h
new file mode 100644
index 000000000..8668b9931
--- /dev/null
+++ b/src/util/max_cliques.h
@@ -0,0 +1,140 @@
+/*++
+Copyright (c) 2016 Microsoft Corporation
+
+Module Name:
+
+    max_cliques.h
+
+Abstract:
+
+    Utility for enumerating locally maximal sub cliques.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2016-11-18
+
+Notes:
+
+
+--*/
+
+#include "vector.h"
+#include "uint_set.h"
+
+class max_cliques_plugin {
+public:
+    virtual unsigned operator()(unsigned i) = 0;
+};
+
+template<class T>
+class max_cliques : public T {
+    vector<unsigned_vector> m_next, m_tc;
+    uint_set                m_reachable[2];
+    uint_set                m_seen1, m_seen2;
+    unsigned_vector         m_todo;
+
+    void get_reachable(unsigned p, uint_set const& goal, uint_set& reachable) {
+        m_seen1.reset();
+        m_todo.reset();
+        m_todo.push_back(p);
+        for (unsigned i = 0; i < m_todo.size(); ++i) {
+            p = m_todo[i];
+            if (m_seen1.contains(p)) {
+                continue;
+            }
+            m_seen1.insert(p);
+            if (m_seen2.contains(p)) {
+                unsigned_vector const& tc = m_tc[p];
+                for (unsigned j = 0; j < tc.size(); ++j) {
+                    unsigned np = tc[j];
+                    if (goal.contains(np)) {
+                        reachable.insert(np);
+                    }
+                }
+            }
+            else {
+                unsigned np = negate(p);
+                if (goal.contains(np)) {
+                    reachable.insert(np);
+                }
+                m_todo.append(next(np));
+            }
+        }
+        for (unsigned i = m_todo.size(); i > 0; ) {
+            --i;
+            p = m_todo[i];
+            if (m_seen2.contains(p)) {
+                continue;
+            }
+            m_seen2.insert(p);
+            unsigned np = negate(p);
+            unsigned_vector& tc = m_tc[p];
+            if (goal.contains(np)) {
+                tc.push_back(np);
+            }
+            else {
+                unsigned_vector const& succ = next(np);
+                for (unsigned j = 0; j < succ.size(); ++j) {
+                    tc.append(m_tc[succ[j]]);
+                }
+            }
+        }
+    }
+
+    
+
+
+
+    unsigned_vector const& next(unsigned vertex) const { return m_next[vertex]; }
+    
+public:
+    max_cliques() {}
+
+    void add_edge(unsigned src, unsigned dst) {
+        m_next.reserve(std::max(src, dst) + 1);
+        m_next.reserve(std::max(negate(src), negate(dst)) + 1);
+        m_next[src].push_back(dst);
+        m_next[dst].push_back(src);
+    }
+
+    void cliques(unsigned_vector const& ps, vector<unsigned_vector>& cliques) {     
+        unsigned max = 0;
+        unsigned num_ps = ps.size();
+        for (unsigned i = 0; i < num_ps; ++i) {
+            unsigned  p = ps[i];
+            unsigned np = negate(p);
+            max = std::max(max, std::max(np, p) + 1);
+        }
+        m_next.reserve(max);
+        m_tc.reserve(max);
+        unsigned_vector clique;
+        uint_set vars;
+        for (unsigned i = 0; i < num_ps; ++i) {
+            vars.insert(ps[i]);
+        }
+
+        while (!vars.empty()) {
+            clique.reset();
+            bool turn = false;
+            m_reachable[turn] = vars;
+            while (!m_reachable[turn].empty()) {
+                unsigned p = *m_reachable[turn].begin();
+                m_reachable[turn].remove(p);
+                vars.remove(p);
+                clique.push_back(p);
+                if (m_reachable[turn].empty()) {
+                    break;
+                }
+                m_reachable[!turn].reset();
+                get_reachable(p, m_reachable[turn], m_reachable[!turn]);
+                turn = !turn;
+            }
+            if (clique.size() > 1) {
+                std::cout << clique.size() << "\n";
+                cliques.push_back(clique);
+            }
+        }
+    }
+
+
+};
diff --git a/src/util/sorting_network.h b/src/util/sorting_network.h
index 87d8bbf3f..2c819db04 100644
--- a/src/util/sorting_network.h
+++ b/src/util/sorting_network.h
@@ -744,6 +744,7 @@ Notes:
             return vc_cmp()*std::min(a-1,b);
         }
         
+    public:
         void sorting(unsigned n, literal const* xs, literal_vector& out) {
             TRACE("pb", tout << "sorting: " << n << "\n";);
             switch(n) {
@@ -773,8 +774,9 @@ Notes:
             TRACE("pb", tout << "sorting: " << n << "\n";
                   pp(tout << "in:", n, xs) << "\n"; 
                   pp(tout << "out:", out) << "\n";);
-
         }
+
+    private:
         vc vc_sorting(unsigned n) {
             switch(n) {
             case 0: return vc(0,0);
diff --git a/src/util/uint_set.h b/src/util/uint_set.h
index 525638f4f..e78a4b0b6 100644
--- a/src/util/uint_set.h
+++ b/src/util/uint_set.h
@@ -163,10 +163,11 @@ public:
     class iterator {
         uint_set const* m_set;
         unsigned  m_index;
+        unsigned  m_last;
 
-        bool invariant() const { return m_index <= m_set->get_max_elem(); }
+        bool invariant() const { return m_index <= m_last; }
 
-        bool at_end() const { return m_index == m_set->get_max_elem(); }
+        bool at_end() const { return m_index == m_last; }
 
         void scan_idx() {
             SASSERT(invariant());
@@ -200,7 +201,7 @@ public:
         }
     public:
         iterator(uint_set const& s, bool at_end): 
-            m_set(&s), m_index(at_end?s.get_max_elem():0) {
+            m_set(&s), m_index(at_end?s.get_max_elem():0), m_last(s.get_max_elem()) {
             scan();
             SASSERT(invariant());
           }
@@ -212,6 +213,7 @@ public:
         iterator & operator=(iterator const& other) { 
             m_set = other.m_set;
             m_index = other.m_index;
+            m_last = other.m_last;
             return *this;
         }
     };