diff --git a/src/opt/inc_sat_solver.cpp b/src/opt/inc_sat_solver.cpp
index 5f121726a..85fef687a 100644
--- a/src/opt/inc_sat_solver.cpp
+++ b/src/opt/inc_sat_solver.cpp
@@ -57,7 +57,7 @@ public:
     virtual lbool check_sat(unsigned num_assumptions, expr * const * assumptions) {
         SASSERT(num_assumptions == 0);
         
-        m_solver.pop(m_solver.scope_lvl());        
+        m_solver.pop_to_base_level();
         goal_ref_buffer result;
         proof_converter_ref pc;   
         model_converter_ref mc;   
@@ -128,13 +128,13 @@ public:
         m_preprocess->set_cancel(f);
     }
     virtual void push() {
-        IF_VERBOSE(0, verbose_stream() << "push ignored\n";);
+        m_solver.user_push();
     }
     virtual void pop(unsigned n) {
-        IF_VERBOSE(0, verbose_stream() << "pop ignored\n";);
+        m_solver.user_pop(n);
     }
     virtual unsigned get_scope_level() const {
-        return 0;
+        return m_solver.scope_lvl();
     }
     virtual void assert_expr(expr * t, expr * a) {
         if (a) {
diff --git a/src/sat/sat_solver.cpp b/src/sat/sat_solver.cpp
index c357f7a29..bf6d0953f 100644
--- a/src/sat/sat_solver.cpp
+++ b/src/sat/sat_solver.cpp
@@ -140,7 +140,16 @@ namespace sat {
             for (unsigned i = 0; i < num_lits; i++)
                 SASSERT(m_eliminated[lits[i].var()] == false);
         });
-        mk_clause_core(num_lits, lits, false);
+        
+        if (m_user_scope_literals.empty()) {
+            mk_clause_core(num_lits, lits, false);
+        }
+        else {
+            m_aux_literals.reset();
+            m_aux_literals.append(num_lits, lits);
+            m_aux_literals.append(m_user_scope_literals);
+            mk_clause_core(m_aux_literals.size(), m_aux_literals.c_ptr(), false);
+        }
     }
 
     void solver::mk_clause(literal l1, literal l2) {
@@ -686,6 +695,7 @@ namespace sat {
     //
     // -----------------------
     lbool solver::check(unsigned num_lits, literal const* lits) {
+        pop_to_base_level();
         IF_VERBOSE(2, verbose_stream() << "(sat.sat-solver using the efficient SAT solver)\n";);
         SASSERT(scope_lvl() == 0);
 #ifdef CLONE_BEFORE_SOLVING
@@ -716,7 +726,7 @@ namespace sat {
                 m_restart_threshold       = m_config.m_restart_initial;
             }
 
-            // iff3_finder(*this)();
+            // iff3_finder(*this)();            
             simplify_problem();
 
             if (inconsistent()) return l_false;
@@ -858,18 +868,27 @@ namespace sat {
     }
 
     void solver::init_assumptions(unsigned num_lits, literal const* lits) {
-        if (num_lits == 0) {
+        if (num_lits == 0 && m_user_scope_literals.empty()) {
             return;
         }
-        push();
         m_assumptions.reset();
-        m_assumption_set.reset();
+        m_assumption_set.reset();        
+        push();
+
+        TRACE("sat", display(tout););
+#define _INSERT_LIT(_l_)                     \
+        SASSERT(is_external((_l_).var()));   \
+        m_assumption_set.insert(_l_);        \
+        m_assumptions.push_back(_l_);        \
+        mk_clause_core(1, &(_l_), false);    \
+
         for (unsigned i = 0; i < num_lits; ++i) {
-            literal l = lits[i];
-            SASSERT(is_external(l.var()));
-            m_assumption_set.insert(l);
-            m_assumptions.push_back(l);
-            mk_clause(1, &l); 
+            literal lit = lits[i];
+            _INSERT_LIT(lit);
+        }
+        for (unsigned i = 0; i < m_user_scope_literals.size(); ++i) {
+            literal nlit = ~m_user_scope_literals[i];
+            _INSERT_LIT(nlit);
         }
         TRACE("sat", display(tout););
     }
@@ -879,7 +898,7 @@ namespace sat {
             push();
             for (unsigned i = 0; i < m_assumptions.size(); ++i) {
                 literal l = m_assumptions[i];
-                mk_clause(1, &l); 
+                mk_clause_core(1, &l, false); 
             }
         }
     }
@@ -911,6 +930,12 @@ namespace sat {
        \brief Apply all simplifications.
     */
     void solver::simplify_problem() {
+
+        if (tracking_assumptions()) {
+            // NB. simplification is disabled when tracking assumptions.
+            return;
+        }
+
         SASSERT(scope_lvl() == 0);
 
         m_cleaner();
@@ -2110,6 +2135,71 @@ namespace sat {
         m_clauses_to_reinit.shrink(j);
     }
 
+    // 
+    // All new clauses that are added to the solver
+    // are relative to the user-scope literals.
+    // 
+
+    void solver::user_push() {
+        literal lit;
+        if (m_user_scope_literal_pool.empty()) {
+            bool_var new_v = mk_var(true, false);
+            lit = literal(new_v, false);
+        }
+        else {
+            lit = m_user_scope_literal_pool.back();
+            m_user_scope_literal_pool.pop_back();
+        }
+        m_user_scope_literals.push_back(lit);
+    }
+
+    void solver::gc_lit(clause_vector &clauses, literal lit) {
+        unsigned j = 0;
+        for (unsigned i = 0; i < clauses.size(); ++i) {
+            clause & c = *(clauses[i]);
+            if (c.contains(lit)) {
+                dettach_clause(c);
+                del_clause(c);
+            }
+            else {
+                clauses[j] = &c;
+                ++j;
+            }
+        }
+        clauses.shrink(j);
+    }
+
+    void solver::gc_bin(bool learned, literal nlit) {
+        m_user_bin_clauses.reset();
+        collect_bin_clauses(m_user_bin_clauses, learned);
+        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;
+            if (nlit == l1 || nlit == l2) {
+                dettach_bin_clause(l1, l2, learned);
+            }
+        }
+    }
+
+    void solver::user_pop(unsigned num_scopes) {
+        pop_to_base_level();
+        while (num_scopes > 0) {
+            literal lit = m_user_scope_literals.back();
+            m_user_scope_literal_pool.push_back(lit);   
+            m_user_scope_literals.pop_back();
+            gc_lit(m_learned, lit);
+            gc_lit(m_clauses, lit);
+            gc_bin(true, lit);
+            gc_bin(false, lit);
+            TRACE("sat", tout << "gc: " << lit << "\n"; display(tout););
+            --num_scopes;
+        }
+    }
+
+    void solver::pop_to_base_level() {
+        pop(scope_lvl());
+    }
+
     // -----------------------
     //
     // Misc
diff --git a/src/sat/sat_solver.h b/src/sat/sat_solver.h
index 48067cc48..8c39599bb 100644
--- a/src/sat/sat_solver.h
+++ b/src/sat/sat_solver.h
@@ -224,6 +224,7 @@ namespace sat {
             if (m_cancel) throw solver_exception(Z3_CANCELED_MSG);
             if (memory::get_allocation_size() > m_config.m_max_memory) throw solver_exception(Z3_MAX_MEMORY_MSG);
         }
+        typedef std::pair<literal, literal> bin_clause;
     protected:
         watch_list & get_wlist(literal l) { return m_watches[l.index()]; }
         watch_list const & get_wlist(literal l) const { return m_watches[l.index()]; }
@@ -350,13 +351,21 @@ namespace sat {
         //
         // -----------------------
         void push();
-    public:
         void pop(unsigned num_scopes);
 
-    protected:
         void unassign_vars(unsigned old_sz);
         void reinit_clauses(unsigned old_sz);
 
+        literal_vector m_user_scope_literals;
+        literal_vector m_user_scope_literal_pool;
+        literal_vector m_aux_literals;
+        svector<bin_clause> m_user_bin_clauses;
+        void gc_lit(clause_vector& clauses, literal lit);
+        void gc_bin(bool learned, literal nlit);
+    public:
+        void user_push();
+        void user_pop(unsigned num_scopes);
+        void pop_to_base_level();
         // -----------------------
         //
         // Simplification
@@ -400,7 +409,6 @@ namespace sat {
         clause * const * end_clauses() const { return m_clauses.end(); }
         clause * const * begin_learned() const { return m_learned.begin(); }
         clause * const * end_learned() const { return m_learned.end(); }
-        typedef std::pair<literal, literal> bin_clause;
         void collect_bin_clauses(svector<bin_clause> & r, bool learned) const;
 
         // -----------------------
diff --git a/src/sat/tactic/sat_tactic.cpp b/src/sat/tactic/sat_tactic.cpp
index 8b575c177..e4d5e6df5 100644
--- a/src/sat/tactic/sat_tactic.cpp
+++ b/src/sat/tactic/sat_tactic.cpp
@@ -116,7 +116,7 @@ class sat_tactic : public tactic {
 #if 0
                 IF_VERBOSE(TACTIC_VERBOSITY_LVL, verbose_stream() << "\"formula constains interpreted atoms, recovering formula from sat solver...\"\n";);
 #endif
-                m_solver.pop(m_solver.scope_lvl());
+                m_solver.pop_to_base_level();
                 m_sat2goal(m_solver, map, m_params, *(g.get()), mc);
             }
             g->inc_depth();
diff --git a/src/test/main.cpp b/src/test/main.cpp
index 3b0179944..d97a94a16 100644
--- a/src/test/main.cpp
+++ b/src/test/main.cpp
@@ -219,6 +219,7 @@ int main(int argc, char ** argv) {
     TST(sorting_network);
     TST(theory_pb);
     TST(simplex);
+    TST(sat_user_scope);
     //TST_ARGV(hs);
 }
 
diff --git a/src/test/sat_user_scope.cpp b/src/test/sat_user_scope.cpp
new file mode 100644
index 000000000..e39059563
--- /dev/null
+++ b/src/test/sat_user_scope.cpp
@@ -0,0 +1,102 @@
+#include "sat_solver.h"
+#include "util.h"
+
+typedef sat::literal_vector clause_t;
+typedef vector<clause_t> clauses_t;
+typedef vector<clauses_t> trail_t;
+
+// [ [c1, c2, ..], [ ...] ]
+
+static unsigned s_num_vars = 6;
+static unsigned s_num_clauses_per_frame = 8;
+static unsigned s_num_frames = 7;
+
+static void add_literal(random_gen& r, clause_t& c) {
+    c.push_back(sat::literal(r(s_num_vars) + 1, r(2) == 0));
+}
+
+static clause_t& last_clause(trail_t& t) {
+    return t.back().back();
+}
+
+static void add_clause(sat::solver& s, random_gen& r, trail_t& t) {
+    t.back().push_back(sat::literal_vector());
+    clause_t& cls = last_clause(t);
+    for (unsigned i = 0; i < 3; ++i) {
+        add_literal(r, cls);
+    }
+    s.mk_clause(cls.size(), cls.c_ptr());
+}
+
+static void display_state(std::ostream& out, sat::solver& s, trail_t& t) {
+    s.display(out);
+}
+
+static void pop_user_scope(sat::solver& s, trail_t& t) {
+    std::cout << "pop\n";
+    s.user_pop(1);
+    t.pop_back();
+}
+
+static void push_user_scope(sat::solver& s, trail_t& t) {
+    std::cout << "push\n";
+    s.user_push();
+    t.push_back(clauses_t());
+}
+
+static void init_vars(sat::solver& s) {
+    for (unsigned i = 0; i <= s_num_vars; ++i) {
+        s.mk_var();
+    }
+}
+
+static void check_coherence(sat::solver& s1, trail_t& t) {
+    params_ref p;
+    sat::solver s2(p, 0);
+    init_vars(s2);
+    sat::literal_vector cls;
+    for (unsigned i = 0; i < t.size(); ++i) {
+        clauses_t& clss = t[i];
+        for (unsigned j = 0; j < clss.size(); ++j) {
+            cls.reset();
+            cls.append(clss[j]);
+            s2.mk_clause(cls.size(), cls.c_ptr());
+        }
+    }
+    lbool is_sat1 = s1.check();
+    lbool is_sat2 = s2.check();
+    if (is_sat1 != is_sat2) {
+        s1.display(std::cout);
+        s2.display(std::cout);
+    }
+    std::cout << is_sat1 << "\n";
+    SASSERT(is_sat1 == is_sat2);
+}
+
+void tst_sat_user_scope() {
+    random_gen r(0);
+    trail_t trail;
+    params_ref p;
+    sat::solver s(p, 0);  // incremental solver
+    init_vars(s);
+    while (true) {
+        for (unsigned i = 0; i < s_num_frames; ++i) {
+            // push 3 frames, pop 2
+            for (unsigned k = 0; k < 3; ++k) {
+                push_user_scope(s, trail);
+                for (unsigned j = 0; j < s_num_clauses_per_frame; ++j) {
+                    add_clause(s, r, trail);
+                }
+                check_coherence(s, trail);
+            }
+            for (unsigned k = 0; k < 2; ++k) {
+                pop_user_scope(s, trail);
+                check_coherence(s, trail);
+            }
+        }
+        for (unsigned i = 0; i < s_num_frames; ++i) {
+            pop_user_scope(s, trail);
+            check_coherence(s, trail);
+        }
+    }
+}