diff --git a/lib/pdr_context.cpp b/lib/pdr_context.cpp
index b24c6fa1c..1454d79f5 100644
--- a/lib/pdr_context.cpp
+++ b/lib/pdr_context.cpp
@@ -395,7 +395,6 @@ namespace pdr {
         lbool is_sat = m_solver.check_conjunction_as_assumptions(n.state());
         if (is_sat == l_true && core) {            
             core->reset();
-            model2cube(*model,*core);
             n.set_model(model);
         }
         return is_sat;
@@ -697,34 +696,6 @@ namespace pdr {
         }        
     }
 
-    void pred_transformer::model2cube(app* c, expr* val, expr_ref_vector& res) const {
-        if (m.is_bool(val)) {
-            res.push_back(m.is_true(val)?c:m.mk_not(c));
-        }
-        else {
-            res.push_back(m.mk_eq(c, val));
-        }
-    }
-
-    void pred_transformer::model2cube(const model_core& mdl, func_decl * d, expr_ref_vector& res) const {
-        expr_ref interp(m);
-        get_value_from_model(mdl, d, interp);   
-        app* c = m.mk_const(d);
-        model2cube(c, interp, res);
-    }
-
-    void pred_transformer::model2cube(const model_core & mdl, expr_ref_vector & res) const {
-        unsigned sz = mdl.get_num_constants();
-        for (unsigned i = 0; i < sz; i++) {
-            func_decl * d = mdl.get_constant(i);                        
-            SASSERT(d->get_arity()==0);
-            if (!m_solver.is_aux_symbol(d)) {
-                model2cube(mdl, d, res);
-            }
-        }   
-    }
-
-
     // ----------------
     // model_node
 
@@ -1103,11 +1074,9 @@ namespace pdr {
           m_inductive_lvl(0),
           m_cancel(false)
     {
-        m_use_model_generalizer = m_params.get_bool("use-model-generalizer", false);
     }
 
     context::~context() {
-        reset_model_generalizers();
         reset_core_generalizers();
         reset();
     }
@@ -1169,7 +1138,6 @@ namespace pdr {
 
     void context::update_rules(datalog::rule_set& rules) {
         decl2rel rels;
-        init_model_generalizers(rules);
         init_core_generalizers(rules);
         init_rules(rules, rels); 
         decl2rel::iterator it = rels.begin(), end = rels.end();
@@ -1294,18 +1262,6 @@ namespace pdr {
     };
 
 
-    void context::reset_model_generalizers() {
-        std::for_each(m_model_generalizers.begin(), m_model_generalizers.end(), delete_proc<model_generalizer>());
-        m_model_generalizers.reset();
-    }
-
-    void context::init_model_generalizers(datalog::rule_set& rules) {
-        reset_model_generalizers();
-        if (m_use_model_generalizer) {
-            m_model_generalizers.push_back(alloc(model_evaluation_generalizer, *this, m));
-        }
-    }
-
     void context::reset_core_generalizers() {
         std::for_each(m_core_generalizers.begin(), m_core_generalizers.end(), delete_proc<core_generalizer>());
         m_core_generalizers.reset();
@@ -1552,11 +1508,7 @@ namespace pdr {
                 }
                 else {
                     TRACE("pdr", tout << "node: " << &n << "\n";); 
-                    for (unsigned i = 0; i < m_model_generalizers.size(); ++i) {
-                        (*m_model_generalizers[i])(n, cube);
-                    }                    
-
-                    create_children(n, m_pm.mk_and(cube));
+                    create_children(n);
                 }
                 break;
             case l_false: {
@@ -1627,45 +1579,6 @@ namespace pdr {
         }
     }
 
-    // create children states from model cube.
-    void context::create_children(model_node& n, expr* model) {
-        if (!m_use_model_generalizer) {
-            create_children2(n);
-            return;
-        }
-        expr_ref_vector literals(m), sub_lits(m);
-        expr_ref o_cube(m), n_cube(m);
-        datalog::flatten_and(model, literals);
-        ptr_vector<func_decl> preds;
-        unsigned level = n.level();
-        SASSERT(level > 0);
-        n.pt().find_predecessors(n.model(), preds);
-        n.pt().remove_predecessors(literals);
-        TRACE("pdr", 
-              model_v2_pp(tout, n.model());
-              tout << "Model cube\n";
-              tout << mk_pp(model, m) << "\n";
-              tout << "Predecessors\n";
-              for (unsigned i = 0; i < preds.size(); ++i) {
-                  tout << preds[i]->get_name() << "\n";
-              }
-             );
-        
-        for (unsigned i = 0; i < preds.size(); ++i) {            
-            pred_transformer& pt = *m_rels.find(preds[i]);
-            SASSERT(pt.head() == preds[i]);
-            assign_ref_vector(sub_lits, literals);
-            m_pm.filter_o_atoms(sub_lits, i);            
-            o_cube = m_pm.mk_and(sub_lits);
-            m_pm.formula_o2n(o_cube, n_cube, i);
-            model_node* child = alloc(model_node, &n, n_cube, pt, level-1);
-            ++m_stats.m_num_nodes;
-            m_search.add_leaf(*child);            
-        }
-        check_pre_closed(n);
-        
-        TRACE("pdr", m_search.display(tout););
-    }
 
     /**
        \brief create children states from model cube.
@@ -1707,7 +1620,7 @@ namespace pdr {
        - Create sub-goals for L0 and L1.
 
     */
-    void context::create_children2(model_node& n) {        
+    void context::create_children(model_node& n) {        
         SASSERT(n.level() > 0);
  
         pred_transformer& pt = n.pt();
@@ -1723,12 +1636,17 @@ namespace pdr {
                    verbose_stream() << "Phi:\n" << mk_pp(phi, m) << "\n";);
                       
         model_evaluator mev(m);
-        expr_ref_vector mdl(m), forms(m);
+        expr_ref_vector mdl(m), forms(m), Phi(m);
         forms.push_back(T);
         forms.push_back(phi);
         datalog::flatten_and(forms);        
         ptr_vector<expr> forms1(forms.size(), forms.c_ptr());
-        expr_ref_vector Phi = mev.minimize_literals(forms1, M);
+        if (m_params.get_bool(":use-model-generalizer", false)) {
+            Phi.append(mev.minimize_model(forms1, M));
+        }
+        else {
+            Phi.append(mev.minimize_literals(forms1, M));
+        }
         ptr_vector<func_decl> preds;
         pt.find_predecessors(r, preds);
         pt.remove_predecessors(Phi);
@@ -1834,9 +1752,6 @@ namespace pdr {
         st.update("PDR max depth", m_stats.m_max_depth);
         m_pm.collect_statistics(st);
 
-        for (unsigned i = 0; i < m_model_generalizers.size(); ++i) {
-            m_model_generalizers[i]->collect_statistics(st);
-        }
         for (unsigned i = 0; i < m_core_generalizers.size(); ++i) {
             m_core_generalizers[i]->collect_statistics(st);
         }
diff --git a/lib/pdr_context.h b/lib/pdr_context.h
index 15124e2cb..cd56c7536 100644
--- a/lib/pdr_context.h
+++ b/lib/pdr_context.h
@@ -98,9 +98,6 @@ namespace pdr {
         void init_atom(decl2rel const& pts, app * atom, app_ref_vector& var_reprs, expr_ref_vector& conj, unsigned tail_idx);
         void ground_free_vars(expr* e, app_ref_vector& vars, ptr_vector<app>& aux_vars);
 
-        void model2cube(const model_core& md, func_decl * d, expr_ref_vector& res) const;
-        void model2cube(app* c, expr* val, expr_ref_vector& res) const;
-
         void simplify_formulas(tactic& tac, expr_ref_vector& fmls);
 
         // Debugging
@@ -157,8 +154,6 @@ namespace pdr {
         manager& get_pdr_manager() const { return pm; }
         ast_manager& get_manager() const { return m; }
 
-        void model2cube(const model_core & mdl, expr_ref_vector & res) const;
-
         void add_premises(decl2rel const& pts, unsigned lvl, expr_ref_vector& r);
 
         void close(expr* e);
@@ -266,18 +261,6 @@ namespace pdr {
 
     class context;
 
-    // 'state' is satisifiable with predecessor 'cube'. 
-    // Generalize predecessor still forcing satisfiability.
-    class model_generalizer {
-    protected:
-        context& m_ctx;
-    public:
-        model_generalizer(context& ctx): m_ctx(ctx) {}
-        virtual ~model_generalizer() {}
-        virtual void operator()(model_node& n, expr_ref_vector& cube) = 0;
-        virtual void collect_statistics(statistics& st) {}
-    };
-
     // 'state' is unsatisfiable at 'level' with 'core'. 
     // Minimize or weaken core.
     class core_generalizer {
@@ -317,9 +300,7 @@ namespace pdr {
         pred_transformer*    m_query;
         model_search         m_search;
         lbool                m_last_result;
-        bool                 m_use_model_generalizer;
         unsigned             m_inductive_lvl;
-        ptr_vector<model_generalizer> m_model_generalizers;
         ptr_vector<core_generalizer>  m_core_generalizers;
         stats                m_stats;
         volatile bool        m_cancel;
@@ -336,8 +317,7 @@ namespace pdr {
         void check_pre_closed(model_node& n);
         void expand_node(model_node& n);
         lbool expand_state(model_node& n, expr_ref_vector& cube);
-        void create_children(model_node& n, expr* model);
-        void create_children2(model_node& n);
+        void create_children(model_node& n);
         expr_ref mk_sat_answer() const;
         expr_ref mk_unsat_answer() const;
         
@@ -347,7 +327,6 @@ namespace pdr {
 
         // Initialization
         class classifier_proc;
-        void init_model_generalizers(datalog::rule_set& rules); 
         void init_core_generalizers(datalog::rule_set& rules);
 
         bool check_invariant(unsigned lvl);
@@ -359,7 +338,6 @@ namespace pdr {
 
         void simplify_formulas();
 
-        void reset_model_generalizers();
         void reset_core_generalizers();
 
     public:       
diff --git a/lib/pdr_generalizers.cpp b/lib/pdr_generalizers.cpp
index 0ba4f6260..dc73148b2 100644
--- a/lib/pdr_generalizers.cpp
+++ b/lib/pdr_generalizers.cpp
@@ -29,19 +29,6 @@ Revision History:
 namespace pdr {
 
 
-    //
-    // eliminate conjuncts from cube as long as state is satisfied.
-    // 
-    void model_evaluation_generalizer::operator()(model_node& n, expr_ref_vector& cube) {
-        expr_ref_vector forms(cube.get_manager());
-        forms.push_back(n.state());
-        forms.push_back(n.pt().transition());
-        datalog::flatten_and(forms);
-        ptr_vector<expr> forms1(forms.size(), forms.c_ptr());
-        model_ref mdl = n.model_ptr();
-        m_model_evaluator.minimize_model(forms1, mdl, cube);
-    }
-
     //
     // main propositional induction generalizer.
     // drop literals one by one from the core and check if the core is still inductive.
diff --git a/lib/pdr_generalizers.h b/lib/pdr_generalizers.h
index 2994beb96..3b9851ca5 100644
--- a/lib/pdr_generalizers.h
+++ b/lib/pdr_generalizers.h
@@ -25,14 +25,6 @@ Revision History:
 
 namespace pdr {
 
-    class model_evaluation_generalizer : public model_generalizer {        
-        model_evaluator m_model_evaluator;
-    public:
-        model_evaluation_generalizer(context& ctx, ast_manager& m) : model_generalizer(ctx), m_model_evaluator(m) {}
-        virtual ~model_evaluation_generalizer() {}
-        virtual void operator()(model_node& n, expr_ref_vector& cube);
-    };
-
     class core_bool_inductive_generalizer : public core_generalizer {
         unsigned m_failure_limit;
     public:
diff --git a/lib/pdr_util.cpp b/lib/pdr_util.cpp
index e9b15c790..13f2dbb29 100644
--- a/lib/pdr_util.cpp
+++ b/lib/pdr_util.cpp
@@ -90,33 +90,6 @@ std::string pp_cube(unsigned sz, expr * const * lits, ast_manager& m) {
 //
 
 
-
-bool model_evaluator::get_assignment(expr* e, expr*& var, expr*& val) {
-    if (m.is_eq(e, var, val)) {
-        if (!is_uninterp(var)) {
-            std::swap(var, val);
-        }
-        if (m.is_true(val) || m.is_false(val) || m_arith.is_numeral(val)) {
-            return true;
-        }
-        TRACE("pdr_verbose", tout << "no value for " << mk_pp(val, m) << "\n";);
-        return false;
-    }
-    else if (m.is_not(e, var)) {
-        val = m.mk_false();
-        return true;
-    }
-    else if (m.is_bool(e)) {
-        val = m.mk_true();
-        var = e;
-        return true;
-    }
-    else {
-        TRACE("pdr_verbose", tout << "no value set of " << mk_pp(e, m) << "\n";);
-        return false;
-    }
-}
-
 void model_evaluator::assign_value(expr* e, expr* val) {
     rational r;
     if (m.is_true(val)) {
@@ -166,7 +139,7 @@ void model_evaluator::reset() {
     m_model = 0;
 }
 
-void model_evaluator::minimize_model(ptr_vector<expr> const & formulas, model_ref& mdl, expr_ref_vector & model) {
+expr_ref_vector model_evaluator::minimize_model(ptr_vector<expr> const & formulas, model_ref& mdl) {
     setup_model(mdl);
 
     TRACE("pdr_verbose", 
@@ -174,7 +147,7 @@ void model_evaluator::minimize_model(ptr_vector<expr> const & formulas, model_re
           for (unsigned i = 0; i < formulas.size(); ++i) tout << mk_pp(formulas[i], m) << "\n"; 
           );
 
-    prune_by_cone_of_influence(formulas, model);
+    expr_ref_vector model = prune_by_cone_of_influence(formulas);
     TRACE("pdr_verbose",
           tout << "pruned model:\n";
           for (unsigned i = 0; i < model.size(); ++i) tout << mk_pp(model[i].get(), m) << "\n";);
@@ -185,6 +158,8 @@ void model_evaluator::minimize_model(ptr_vector<expr> const & formulas, model_re
         setup_model(mdl);
         VERIFY(check_model(formulas));
         reset(););
+
+    return model;
 }
 
 expr_ref_vector model_evaluator::minimize_literals(ptr_vector<expr> const& formulas, model_ref& mdl) {
@@ -340,7 +315,7 @@ void model_evaluator::collect(ptr_vector<expr> const& formulas, ptr_vector<expr>
     m_visited.reset();
 }
 
-void model_evaluator::prune_by_cone_of_influence(ptr_vector<expr> const & formulas, expr_ref_vector& model) {
+expr_ref_vector model_evaluator::prune_by_cone_of_influence(ptr_vector<expr> const & formulas) {
     ptr_vector<expr> tocollect;
     collect(formulas, tocollect);
     m1.reset();
@@ -349,19 +324,23 @@ void model_evaluator::prune_by_cone_of_influence(ptr_vector<expr> const & formul
         TRACE("pdr_verbose", tout << "collect: " << mk_pp(tocollect[i], m) << "\n";);
         for_each_expr(*this, m_visited, tocollect[i]);
     }
-    unsigned sz1 = model.size();
-    for (unsigned i = 0; i < model.size(); ++i) {
-        expr* e = model[i].get(), *var, *val;
-        if (get_assignment(e, var, val)) {
-            if (!m_visited.is_marked(var)) {
-                model[i] = model.back();
-                model.pop_back(); 
-                --i;
-            }
+    unsigned sz = m_model->get_num_constants();
+    expr_ref e(m), eq(m);
+    expr_ref_vector model(m);
+    bool_rewriter rw(m);
+    for (unsigned i = 0; i < sz; i++) {
+        func_decl * d = m_model->get_constant(i); 
+        expr* val = m_model->get_const_interp(d);
+        e = m.mk_const(d);
+        if (m_visited.is_marked(e)) {
+            rw.mk_eq(e, val, eq);
+            model.push_back(eq);
         }
     }
     m_visited.reset();
-    TRACE("pdr", tout << sz1 << " ==> " << model.size() << "\n";);
+    TRACE("pdr", tout << sz << " ==> " << model.size() << "\n";);
+    return model;
+
 }
 
 void model_evaluator::eval_arith(app* e) {
diff --git a/lib/pdr_util.h b/lib/pdr_util.h
index 11f780a7e..4f6ab1ad3 100644
--- a/lib/pdr_util.h
+++ b/lib/pdr_util.h
@@ -194,10 +194,9 @@ class model_evaluator {
     void reset();
     void setup_model(model_ref& model);
     void assign_value(expr* e, expr* v);
-    bool get_assignment(expr* e, expr*& var, expr*& val);
     void collect(ptr_vector<expr> const& formulas, ptr_vector<expr>& tocollect);
     void process_formula(app* e, ptr_vector<expr>& todo, ptr_vector<expr>& tocollect);
-    void prune_by_cone_of_influence(ptr_vector<expr> const & formulas, expr_ref_vector& model);
+    expr_ref_vector prune_by_cone_of_influence(ptr_vector<expr> const & formulas);
     void eval_arith(app* e);
     void eval_basic(app* e);
     void eval_iff(app* e, expr* arg1, expr* arg2);
@@ -230,7 +229,13 @@ protected:
 public:
     model_evaluator(ast_manager& m) : m(m), m_arith(m), m_bv(m), m_refs(m) {}
 
-    virtual void minimize_model(ptr_vector<expr> const & formulas, model_ref& mdl, expr_ref_vector& model);
+    /**
+       \brief extract equalities from model that suffice to satisfy formula.
+
+       \pre model satisfies formulas
+    */
+
+    expr_ref_vector minimize_model(ptr_vector<expr> const & formulas, model_ref& mdl);
 
     /**
        \brief extract literals from formulas that satisfy formulas.
@@ -239,12 +244,6 @@ public:
     */
     expr_ref_vector minimize_literals(ptr_vector<expr> const & formulas, model_ref& mdl);
 
-    /**
-       \brief extract literals from formulas that satisfy formulas.
-
-       \pre model satisfies formulas
-    */
-    expr_ref_vector minimize_literals(ptr_vector<expr> const & formulas, expr_ref_vector const & model);
 
     // for_each_expr visitor.
     void operator()(expr* e) {} 
diff --git a/lib/qe_lite.cpp b/lib/qe_lite.cpp
new file mode 100644
index 000000000..d295327da
--- /dev/null
+++ b/lib/qe_lite.cpp
@@ -0,0 +1,536 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    qe_lite.cpp
+
+Abstract:
+
+    Light weight partial quantifier-elimination procedure
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2012-10-17
+
+Revision History:
+
+ - TBD: integrate Fourier Motzkin elimination
+        integrate Gaussean elimination
+
+--*/
+#include "qe_lite.h"
+#include "expr_abstract.h"
+#include "used_vars.h"
+#include"occurs.h"
+#include"for_each_expr.h"
+#include"rewriter_def.h"
+#include"ast_pp.h"
+#include"ast_ll_pp.h"
+#include"ast_smt2_pp.h"
+#include"tactical.h"
+#include"bool_rewriter.h"
+#include"var_subst.h"
+
+class der2 {
+    ast_manager &   m;
+    var_subst       m_subst;
+    expr_ref_buffer m_new_exprs;
+    
+    ptr_vector<expr> m_map;
+    int_vector       m_pos2var;
+    ptr_vector<var>  m_inx2var;
+    unsigned_vector  m_order;
+    expr_ref_vector  m_subst_map;
+    expr_ref_buffer  m_new_args;
+
+    /**
+       \brief Return true if e can be viewed as a variable disequality. 
+       Store the variable id in v and the definition in t.
+       For example:
+
+          if e is (not (= (VAR 1) T)), then v assigned to 1, and t to T.
+          if e is (iff (VAR 2) T), then v is assigned to 2, and t to (not T).
+              (not T) is used because this formula is equivalent to (not (iff (VAR 2) (not T))),
+              and can be viewed as a disequality.
+    */
+    bool is_var_diseq(expr * e, unsigned num_decls, var *& v, expr_ref & t);
+
+    /**
+       \brief Return true if e can be viewed as a variable equality.
+    */
+    bool is_var_eq(expr * e, unsigned num_decls, var *& v, expr_ref & t);
+
+    bool is_var_def(bool check_eq, expr* e, unsigned num_decls, var*& v, expr_ref& t);
+
+    void get_elimination_order();
+    void create_substitution(unsigned sz);
+    void apply_substitution(quantifier * q, expr_ref & r);
+    void reduce_quantifier1(quantifier * q, expr_ref & r, proof_ref & pr);
+    void elim_unused_vars(expr_ref& r, proof_ref &pr);
+
+public:
+    der2(ast_manager & m):m(m),m_subst(m),m_new_exprs(m),m_subst_map(m),m_new_args(m) {}
+    void operator()(quantifier * q, expr_ref & r, proof_ref & pr);
+    void reduce_quantifier(quantifier * q, expr_ref & r, proof_ref & pr);
+    ast_manager& get_manager() const { return m; }
+};
+
+static bool is_var(expr * e, unsigned num_decls) {
+    return is_var(e) && to_var(e)->get_idx() < num_decls;
+}
+
+static bool is_neg_var(ast_manager & m, expr * e, unsigned num_decls) {
+    expr* e1;
+    return m.is_not(e, e1) && is_var(e1, num_decls);
+}
+
+bool der2::is_var_def(bool check_eq, expr* e, unsigned num_decls, var*& v, expr_ref& t) {
+    if (check_eq) {
+        return is_var_eq(e, num_decls, v, t);
+    }
+    else {
+        return is_var_diseq(e, num_decls, v, t);
+    }    
+}
+
+bool der2::is_var_eq(expr * e, unsigned num_decls, var * & v, expr_ref & t) {
+    expr* lhs, *rhs;
+    
+    // (= VAR t), (iff VAR t), (iff (not VAR) t), (iff t (not VAR)) cases    
+    if (m.is_eq(e, lhs, rhs) || m.is_iff(e, lhs, rhs)) {
+        // (iff (not VAR) t) (iff t (not VAR)) cases
+        if (!is_var(lhs, num_decls) && !is_var(rhs, num_decls) && m.is_bool(lhs)) {
+            if (!is_neg_var(m, lhs, num_decls)) {
+                std::swap(lhs, rhs);
+            }
+            if (!is_neg_var(m, lhs, num_decls)) {
+                return false;
+            }
+            v = to_var(lhs);
+            t = m.mk_not(rhs);
+            m_new_exprs.push_back(t);
+            TRACE("der", tout << mk_pp(e, m) << "\n";);
+            return true;
+        }
+        if (!is_var(lhs, num_decls))
+            std::swap(lhs, rhs);
+        if (!is_var(lhs, num_decls))
+            return false;
+        v = to_var(lhs);
+        t = rhs;
+        TRACE("der", tout << mk_pp(e, m) << "\n";);
+        return true;
+    }
+
+    // (ite cond (= VAR t) (= VAR t2)) case
+    expr* cond, *e2, *e3;
+    if (m.is_ite(e, cond, e2, e3)) {
+        if (is_var_eq(e2, num_decls, v, t)) {
+            expr_ref t2(m);
+            var* v2;
+            if (is_var_eq(e3, num_decls, v2, t2) && v2 == v) {
+                t = m.mk_ite(cond, t, t2);
+                m_new_exprs.push_back(t);
+                return true;
+            }
+        }
+        return false;
+    }
+
+    // VAR = true case
+    if (is_var(e, num_decls)) {
+        t = m.mk_true();
+        v = to_var(e);
+        TRACE("der", tout << mk_pp(e, m) << "\n";);
+        return true;
+    }
+
+    // VAR = false case
+    if (is_neg_var(m, e, num_decls)) {
+        t = m.mk_false();
+        v = to_var(to_app(e)->get_arg(0));
+        TRACE("der", tout << mk_pp(e, m) << "\n";);
+        return true;
+    }
+
+    return false;
+}
+
+/**
+   \brief Return true if \c e is of the form (not (= VAR t)) or (not (iff VAR t)) or 
+                                (iff VAR t) or (iff (not VAR) t) or (VAR IDX) or (not (VAR IDX)).
+   The last case can be viewed 
+*/
+bool der2::is_var_diseq(expr * e, unsigned num_decls, var * & v, expr_ref & t) {
+    expr* e1;
+    if (m.is_not(e, e1)) {
+        return is_var_eq(e, num_decls, v, t);
+    }
+    else if (is_var_eq(e, num_decls, v, t) && m.is_bool(v)) { 
+        bool_rewriter(m).mk_not(t, t);
+        m_new_exprs.push_back(t);
+        return true;
+    }
+    else {
+        return false;
+    }
+}
+
+void der2::elim_unused_vars(expr_ref& r, proof_ref& pr) {
+    if (is_quantifier(r)) {
+        quantifier * q = to_quantifier(r);
+        ::elim_unused_vars(m, q, r);
+        if (m.proofs_enabled()) {
+            proof * p1 = m.mk_elim_unused_vars(q, r);
+            pr = m.mk_transitivity(pr, p1);
+        }
+    }
+}
+
+/**
+   Reduce the set of definitions in quantifier.
+   Then eliminate variables that have become unused
+*/
+void der2::operator()(quantifier * q, expr_ref & r, proof_ref & pr) {
+    TRACE("der", tout << mk_pp(q, m) << "\n";);    
+    pr = 0;
+    r  = q;
+    reduce_quantifier(q, r, pr);    
+    if (r != q) {
+        elim_unused_vars(r, pr);
+    }
+}
+
+void der2::reduce_quantifier(quantifier * q, expr_ref & r, proof_ref & pr) {   
+    r = q;
+    // Keep applying reduce_quantifier1 until r doesn't change anymore
+    do {
+        proof_ref curr_pr(m);
+        q  = to_quantifier(r);
+        reduce_quantifier1(q, r, curr_pr);
+        if (m.proofs_enabled()) {
+            pr = m.mk_transitivity(pr, curr_pr);
+        }
+    } while (q != r && is_quantifier(r));
+
+    m_new_exprs.reset();
+}
+
+void der2::reduce_quantifier1(quantifier * q, expr_ref & r, proof_ref & pr) {    
+    expr * e = q->get_expr();
+    unsigned num_decls = q->get_num_decls();
+    var * v = 0;
+    expr_ref t(m);    
+    unsigned num_args = 1;
+    expr* const* args = &e;
+    if ((q->is_forall() && m.is_or(e)) ||
+        (q->is_exists() && m.is_and(e))) {
+        num_args = to_app(e)->get_num_args();
+        args     = to_app(e)->get_args();
+    }
+
+    unsigned def_count = 0;
+    unsigned largest_vinx = 0;
+    
+    m_map.reset();
+    m_pos2var.reset();
+    m_inx2var.reset();    
+    m_pos2var.reserve(num_args, -1);
+    
+    // Find all definitions
+    for (unsigned i = 0; i < num_args; i++) {
+        if (is_var_def(q->is_exists(), args[i], num_decls, v, t)) {
+            unsigned idx = v->get_idx();
+            if(m_map.get(idx, 0) == 0) {
+                m_map.reserve(idx + 1, 0);
+                m_inx2var.reserve(idx + 1, 0);                
+                m_map[idx] = t;
+                m_inx2var[idx] = v;
+                m_pos2var[i] = idx;
+                def_count++;
+                largest_vinx = std::max(idx, largest_vinx); 
+            }
+        }
+    }
+    
+    if (def_count > 0) {
+        get_elimination_order();
+        SASSERT(m_order.size() <= def_count); // some might be missing because of cycles
+        
+        if (!m_order.empty()) {            
+            create_substitution(largest_vinx + 1);
+            apply_substitution(q, r);
+        }
+        else {
+            r = q;
+        }
+    }
+    else {
+        TRACE("der_bug", tout << "Did not find any diseq\n" << mk_pp(q, m) << "\n";);
+        r = q;
+    }
+ 
+    if (m.proofs_enabled()) {
+        pr = r == q ? 0 : m.mk_der(q, r);
+    }    
+}
+
+static void der_sort_vars(ptr_vector<var> & vars, ptr_vector<expr> & definitions, unsigned_vector & order) {
+    order.reset();
+    
+    // eliminate self loops, and definitions containing quantifiers.
+    bool found = false;
+    for (unsigned i = 0; i < definitions.size(); i++) {
+        var * v  = vars[i];
+        expr * t = definitions[i];
+        if (t == 0 || has_quantifiers(t) || occurs(v, t))
+            definitions[i] = 0;
+        else
+            found = true; // found at least one candidate
+    }
+    
+    if (!found)
+        return;
+
+    typedef std::pair<expr *, unsigned> frame;
+    svector<frame> todo;
+
+    expr_fast_mark1 visiting;
+    expr_fast_mark2 done;
+
+    unsigned vidx, num;
+
+    for (unsigned i = 0; i < definitions.size(); i++) {
+        if (definitions[i] == 0)
+            continue;
+        var * v = vars[i];
+        SASSERT(v->get_idx() == i);
+        SASSERT(todo.empty());
+        todo.push_back(frame(v, 0));
+        while (!todo.empty()) {
+        start:
+            frame & fr = todo.back();
+            expr * t   = fr.first;
+            if (t->get_ref_count() > 1 && done.is_marked(t)) {
+                todo.pop_back();
+                continue;
+            }
+            switch (t->get_kind()) {
+            case AST_VAR:
+                vidx = to_var(t)->get_idx();
+                if (fr.second == 0) {
+                    CTRACE("der_bug", vidx >= definitions.size(), tout << "vidx: " << vidx << "\n";);
+                    // Remark: The size of definitions may be smaller than the number of variables occuring in the quantified formula.
+                    if (definitions.get(vidx, 0) != 0) {
+                        if (visiting.is_marked(t)) {
+                            // cycle detected: remove t
+                            visiting.reset_mark(t);
+                            definitions[vidx] = 0;
+                        }
+                        else {
+                            visiting.mark(t);
+                            fr.second = 1;
+                            todo.push_back(frame(definitions[vidx], 0));
+                            goto start;
+                        }
+                    }
+                }
+                else {
+                    SASSERT(fr.second == 1);
+                    if (definitions.get(vidx, 0) != 0) {
+                        visiting.reset_mark(t);
+                        order.push_back(vidx);
+                    }
+                    else {
+                        // var was removed from the list of candidate vars to elim cycle
+                        // do nothing
+                    }
+                }
+                if (t->get_ref_count() > 1)
+                    done.mark(t);
+                todo.pop_back();
+                break;
+            case AST_QUANTIFIER:
+                UNREACHABLE();
+                todo.pop_back();
+                break;
+            case AST_APP:
+                num = to_app(t)->get_num_args();
+                while (fr.second < num) {
+                    expr * arg = to_app(t)->get_arg(fr.second);
+                    fr.second++;
+                    if (arg->get_ref_count() > 1 && done.is_marked(arg))
+                        continue;
+                    todo.push_back(frame(arg, 0));
+                    goto start;
+                }
+                if (t->get_ref_count() > 1)
+                    done.mark(t);
+                todo.pop_back();
+                break;
+            default:
+                UNREACHABLE();
+                todo.pop_back();
+                break;
+            }
+        }
+    }
+}
+
+void der2::get_elimination_order() {
+    m_order.reset();
+
+    TRACE("top_sort",
+        tout << "DEFINITIONS: " << std::endl;
+        for(unsigned i = 0; i < m_map.size(); i++)
+            if(m_map[i]) tout << "VAR " << i << " = " << mk_pp(m_map[i], m) << std::endl;
+      );
+
+    // der2::top_sort ts(m);
+    der_sort_vars(m_inx2var, m_map, m_order);
+
+    TRACE("der", 
+            tout << "Elimination m_order:" << std::endl;
+            for(unsigned i=0; i<m_order.size(); i++)
+            {
+                if (i != 0) tout << ",";
+                tout << m_order[i];
+            }
+            tout << std::endl;            
+          );
+}
+
+void der2::create_substitution(unsigned sz) {
+    m_subst_map.reset();
+    m_subst_map.resize(sz, 0);
+
+    for(unsigned i = 0; i < m_order.size(); i++) {
+        expr_ref cur(m_map[m_order[i]], m);
+
+        // do all the previous substitutions before inserting
+        expr_ref r(m);
+        m_subst(cur, m_subst_map.size(), m_subst_map.c_ptr(), r);
+
+        unsigned inx = sz - m_order[i]- 1;
+        SASSERT(m_subst_map[inx]==0);
+        m_subst_map[inx] = r;
+    }
+}
+
+void der2::apply_substitution(quantifier * q, expr_ref & r) {
+    expr * e = q->get_expr();
+    unsigned num_args=to_app(e)->get_num_args(); 
+    bool_rewriter rw(m);
+    
+    // get a new expression
+    m_new_args.reset();
+    for(unsigned i = 0; i < num_args; i++) {
+        int x = m_pos2var[i];
+        if (x != -1 && m_map[x] != 0) 
+            continue; // this is a disequality with definition (vanishes)
+                
+        m_new_args.push_back(to_app(e)->get_arg(i));
+    }
+
+    expr_ref t(m);
+    if (q->is_forall()) {
+        rw.mk_or(m_new_args.size(), m_new_args.c_ptr(), t);
+    }
+    else {
+        rw.mk_and(m_new_args.size(), m_new_args.c_ptr(), t);
+    }
+    expr_ref new_e(m);    
+    m_subst(t, m_subst_map.size(), m_subst_map.c_ptr(), new_e);
+    
+    // don't forget to update the quantifier patterns
+    expr_ref_buffer  new_patterns(m);
+    expr_ref_buffer  new_no_patterns(m);
+    for (unsigned j = 0; j < q->get_num_patterns(); j++) {
+        expr_ref new_pat(m);
+        m_subst(q->get_pattern(j), m_subst_map.size(), m_subst_map.c_ptr(), new_pat);
+        new_patterns.push_back(new_pat);
+    }
+
+    for (unsigned j = 0; j < q->get_num_no_patterns(); j++) {
+        expr_ref new_nopat(m);
+        m_subst(q->get_no_pattern(j), m_subst_map.size(), m_subst_map.c_ptr(), new_nopat);
+        new_no_patterns.push_back(new_nopat);
+    }
+
+    r = m.update_quantifier(q, new_patterns.size(), new_patterns.c_ptr(), 
+                            new_no_patterns.size(), new_no_patterns.c_ptr(), new_e);
+}
+
+
+
+
+
+class qe_lite::impl {
+    ast_manager& m;
+    der2         m_der;
+
+public:
+    impl(ast_manager& m): m(m), m_der(m) {}
+    
+    void operator()(app_ref_vector& vars, expr_ref& fml) {
+        expr_ref tmp(fml);
+        quantifier_ref q(m);
+        proof_ref pr(m);     
+        symbol qe_lite("QE");
+        expr_abstract(m, 0, vars.size(), (expr*const*)vars.c_ptr(), fml, tmp);
+        ptr_vector<sort> sorts;
+        svector<symbol> names;
+        for (unsigned i = 0; i < vars.size(); ++i) {
+            sorts.push_back(m.get_sort(vars[i].get()));
+            names.push_back(vars[i]->get_decl()->get_name());
+        }
+        q = m.mk_exists(vars.size(), sorts.c_ptr(), names.c_ptr(), tmp, 1, qe_lite);
+        m_der.reduce_quantifier(q, tmp, pr);
+        // assumes m_der just updates the quantifier and does not change things more.
+        if (is_exists(tmp) && to_quantifier(tmp)->get_qid() == qe_lite) {
+            used_vars used;
+            tmp = to_quantifier(tmp)->get_expr();
+            used.process(tmp);
+            var_subst vs(m, true);
+            vs(tmp, vars.size(), (expr*const*)vars.c_ptr(), fml);
+            // collect set of variables that were used.
+            unsigned j = 0;
+            for (unsigned i = 0; i < vars.size(); ++i) {
+                if (used.contains(vars.size()-i-1)) {
+                    vars[j] = vars[i];
+                    ++j;
+                }
+            }
+            vars.resize(j);            
+        }        
+        else {
+            fml = tmp;
+        }
+    }
+
+    void operator()(expr_ref& fml, proof_ref& pr) {
+        // TODO apply der everywhere as a rewriting rule.
+        // TODO add cancel method.
+        if (is_quantifier(fml)) {
+            m_der(to_quantifier(fml), fml, pr);
+        }
+    }
+
+};
+
+qe_lite::qe_lite(ast_manager& m) {
+    m_impl = alloc(impl, m);
+}
+
+qe_lite::~qe_lite() {
+    dealloc(m_impl);
+}
+
+void qe_lite::operator()(app_ref_vector& vars, expr_ref& fml) {
+    (*m_impl)(vars, fml);
+}
+
+void qe_lite::operator()(expr_ref& fml, proof_ref& pr) {
+    (*m_impl)(fml, pr);
+}
diff --git a/lib/qe_lite.h b/lib/qe_lite.h
new file mode 100644
index 000000000..1a2f98294
--- /dev/null
+++ b/lib/qe_lite.h
@@ -0,0 +1,49 @@
+/*++
+Copyright (c) 2010 Microsoft Corporation
+
+Module Name:
+
+    qe_lite.h
+
+Abstract:
+
+    Light weight partial quantifier-elimination procedures 
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2012-10-17
+
+Revision History:
+
+
+--*/
+
+#ifndef __QE_LITE_H__
+#define __QE_LITE_H__
+
+#include "ast.h"
+
+class qe_lite {
+    class impl;
+    impl * m_impl;
+public:
+    qe_lite(ast_manager& m);
+
+    ~qe_lite();
+
+    /**
+       \brief
+       Apply light-weight quantifier elimination 
+       on constants provided as vector of variables. 
+       Return the updated formula and updated set of variables that were not eliminated.
+
+    */
+    void operator()(app_ref_vector& vars, expr_ref& fml);
+
+    /**
+        \brief full rewriting based light-weight quantifier elimination round.
+    */
+    void operator()(expr_ref& fml, proof_ref& pr);
+};
+
+#endif __QE_LITE_H__