diff --git a/src/qe/qe_term_graph.cpp b/src/qe/qe_term_graph.cpp
new file mode 100644
index 000000000..d0bcc11c4
--- /dev/null
+++ b/src/qe/qe_term_graph.cpp
@@ -0,0 +1,525 @@
+/**++
+Copyright (c) Arie Gurfinkel
+
+Module Name:
+
+    qe_term_graph.cpp
+
+Abstract:
+
+    Equivalence graph of terms
+
+Author:
+
+    Arie Gurfinkel
+
+Notes:
+
+--*/
+
+#include "util/util.h"
+#include "ast/ast_pp.h"
+#include "ast/ast_util.h"
+#include "ast/for_each_expr.h"
+#include "qe/qe_term_graph.h"
+
+namespace qe {
+
+class term {
+    // -- an app represented by this term
+    app* m_app;
+    // -- root of the equivalence class
+    term* m_root;
+    // -- next element in the equivalence class (cyclic linked list)
+    term* m_next;
+    // -- eq class size
+    unsigned m_class_size;
+
+    // -- general purpose mark
+    unsigned m_mark:1;
+    // -- general purpose second mark
+    unsigned m_mark2:1;
+    // -- is an interpreted constant
+    unsigned m_interpreted:1;
+
+    // -- terms that contain this term as a child
+    //ptr_vector<term> m_uses;
+
+    // ptr_vector<term> m_args;
+
+public:
+    term(app* a) : m_app(a), m_root(this), m_next(this),
+                   m_class_size(1), m_mark(false), m_mark2(false),
+                   m_interpreted(false) {}
+
+    ~term() {}
+
+    unsigned get_id() const {return m_app->get_id();}
+
+    bool is_marked() const {return m_mark;}
+    void set_mark(bool v){m_mark = v;}
+    bool is_marked2() const {return m_mark2;}
+    void set_mark2(bool v){m_mark2 = v;}
+
+    bool is_interpreted() const {return m_interpreted;}
+    void mark_as_interpreted() {m_interpreted=true;}
+    app* get_app() const {return m_app;}
+
+    term &get_root() const {return *m_root;}
+    bool is_root() const {return m_root == this;}
+    void set_root(term &r) {m_root = &r;}
+    term &get_next() const {return *m_next;}
+
+    unsigned get_class_size() const {return m_class_size;}
+
+    void merge_eq_class(term &b) {
+        std::swap(this->m_next, b.m_next);
+        m_class_size += b.get_class_size();
+        // -- reset (useful for debugging)
+        b.m_class_size = 0;
+    }
+
+    // -- make this term the root of its equivalence class
+    void mk_root() {
+        if (is_root()) return;
+
+        term *curr = this;
+        do {
+            if (curr->is_root()) {
+                // found previous root
+                SASSERT(curr != this);
+                m_class_size = curr->get_class_size();
+                curr->m_class_size = 0;
+            }
+            curr->set_root(*this);
+            curr = &curr->get_next();
+        }
+        while (curr != this);
+    }
+};
+
+class arith_term_graph_plugin : public term_graph_plugin {
+    term_graph &m_g;
+    ast_manager &m;
+    arith_util m_arith;
+
+public:
+    arith_term_graph_plugin(term_graph &g) :
+        term_graph_plugin (g.get_ast_manager().mk_family_id("arith")),
+        m_g(g), m(g.get_ast_manager()), m_arith(m) {(void)m_g;}
+
+    virtual ~arith_term_graph_plugin() {}
+
+    bool mk_eq_core (expr *_e1, expr *_e2, app_ref &res) {
+        expr *e1, *e2;
+        e1 = _e1;
+        e2 = _e2;
+
+        if (m_arith.is_zero(e1)) {
+            std::swap(e1, e2);
+        }
+        // y + -1*x == 0  --> y = x
+        expr *a0 = 0, *a1 = 0, *x = 0;
+        if (m_arith.is_zero(e2) && m_arith.is_add(e1, a0, a1)) {
+            if (m_arith.is_times_minus_one(a1, x)) {
+                e1 = a0;
+                e2 = x;
+            }
+            else if (m_arith.is_times_minus_one(a0, x)) {
+                e1 = a1;
+                e2 = x;
+            }
+        }
+        res = m.mk_eq(e1, e2);
+        return true;
+    }
+
+    app* mk_le_zero(expr *arg) {
+        expr *e1, *e2, *e3;
+        // XXX currently disabled
+        if (m_arith.is_add(arg, e1, e2)) {
+            // e1-e2<=0 --> e1<=e2
+            if (m_arith.is_times_minus_one(e2, e3)) {
+                return m_arith.mk_le(e1, e3);
+            }
+            // -e1+e2<=0 --> e2<=e1
+            else if (m_arith.is_times_minus_one(e1, e3)) {
+                return m_arith.mk_le(e2, e3);
+            }
+        }
+        return m_arith.mk_le(arg, mk_zero());
+    }
+
+    app* mk_ge_zero(expr *arg) {
+        expr *e1, *e2, *e3;
+        // XXX currently disabled
+        if (m_arith.is_add(arg, e1, e2)) {
+            // e1-e2>=0 --> e1>=e2
+            if (m_arith.is_times_minus_one(e2, e3)) {
+                return m_arith.mk_ge(e1, e3);
+            }
+            // -e1+e2>=0 --> e2>=e1
+            else if (m_arith.is_times_minus_one(e1, e3)) {
+                return m_arith.mk_ge(e2, e3);
+            }
+        }
+        return m_arith.mk_ge(arg, mk_zero());
+    }
+
+    bool mk_le_core (expr *arg1, expr * arg2, app_ref &result) {
+        // t <= -1  ==> t < 0 ==> ! (t >= 0)
+        rational n;
+        if (m_arith.is_int (arg1) && m_arith.is_minus_one (arg2)) {
+            result = m.mk_not (mk_ge_zero (arg1));
+            return true;
+        }
+        else if (m_arith.is_zero(arg2)) {
+            result = mk_le_zero(arg1);
+            return true;
+        }
+        else if (m_arith.is_int(arg1) && m_arith.is_numeral(arg2, n) && n < 0) {
+            // t <= n ==> t < n + 1 ==> ! (t >= n + 1)
+            result = m.mk_not(m_arith.mk_ge(arg1, m_arith.mk_numeral(n+1, true)));
+            return true;
+        }
+        return false;
+    }
+
+    expr * mk_zero () {return m_arith.mk_numeral (rational (0), true);}
+    bool is_one (expr const * n) const {
+        rational val;
+        return m_arith.is_numeral (n, val) && val.is_one ();
+    }
+
+    bool mk_ge_core (expr * arg1, expr * arg2, app_ref &result) {
+        // t >= 1 ==> t > 0 ==> ! (t <= 0)
+        rational n;
+        if (m_arith.is_int (arg1) && is_one (arg2)) {
+            result = m.mk_not (mk_le_zero (arg1));
+            return true;
+        }
+        else if (m_arith.is_zero(arg2)) {
+            result = mk_ge_zero(arg1);
+            return true;
+        }
+        else if (m_arith.is_int(arg1) && m_arith.is_numeral(arg2, n) && n > 0) {
+            // t >= n ==> t > n - 1 ==> ! (t <= n - 1)
+            result = m.mk_not(m_arith.mk_le(arg1, m_arith.mk_numeral(n-1, true)));
+            return true;
+        }
+        return false;
+    }
+
+    virtual app_ref process_lit (app *_lit) {
+        app *lit = _lit;
+        expr *e1, *e2;
+
+        // strip negation
+        bool is_neg = m.is_not(lit);
+        if (is_neg) {
+            lit = to_app(to_app(lit)->get_arg(0));
+        }
+
+        app_ref res(m);
+        res = lit;
+        if (m.is_eq (lit, e1, e2)) {
+            mk_eq_core(e1, e2, res);
+        }
+        else if (m_arith.is_le(lit, e1, e2)) {
+            mk_le_core(e1, e2, res);
+        }
+        else if (m_arith.is_ge(lit, e1, e2)) {
+            mk_ge_core(e1, e2, res);
+        }
+
+        // restore negation
+        if (is_neg) {
+            res = m.mk_not(res);
+        }
+
+        return res;
+    }
+};
+
+term_graph::term_graph(ast_manager &man) : m(man), m_lits(m), m_pinned(m) {
+    m_plugins.register_plugin (alloc(arith_term_graph_plugin, *this));
+}
+term_graph::~term_graph() {
+    reset();
+}
+
+static family_id get_family_id(ast_manager &m, app *lit) {
+    family_id fid = null_family_id;
+
+    expr *e1, *e2, *e3;
+    // strip negation
+    if (!m.is_not (lit, e1)) { e1 = lit; }
+
+    // deal with equality using sort of range
+    if (m.is_eq (e1, e2, e3)) {
+        fid = get_sort (e2)->get_family_id();
+    }
+    // extract family_id of top level app
+    else {
+        fid = to_app(e1)->get_decl()->get_family_id();
+    }
+
+    return fid;
+}
+
+void term_graph::add_lit(app *l) {
+    app_ref lit(m);
+
+    family_id fid = get_family_id (m, l);
+    term_graph_plugin *pin = m_plugins.get_plugin(fid);
+    if (pin) {
+        lit = pin->process_lit(l);
+    } else {
+        lit = l;
+    }
+    m_lits.push_back(lit);
+    internalize_lit(lit);
+}
+
+bool term_graph::is_internalized(app *a) {
+    return m_app2term.contains(a->get_id());
+}
+
+term* term_graph::get_term(app *a) {
+    term *res;
+    return m_app2term.find (a->get_id(), res) ? res : nullptr;
+}
+
+term *term_graph::mk_term(app *a) {
+    term * t = alloc(term, a);
+    if (a->get_num_args() == 0 && m.is_unique_value(a)){
+        t->mark_as_interpreted();
+    }
+
+    m_terms.push_back(t);
+    m_app2term.insert(a->get_id(), t);
+    return t;
+}
+
+term *term_graph::internalize_term(app *t) {
+    term *res = get_term(t);
+
+    if (!res) {
+        for (expr * arg : *t) {
+            SASSERT(is_app(arg));
+            internalize_term(::to_app(arg));
+        }
+        res = mk_term(t);
+    }
+    return res;
+}
+
+void term_graph::internalize_eq(app *a1, app* a2) {
+    internalize_lit(a1);
+    internalize_lit(a2);
+    merge(get_term(a1)->get_root(), get_term(a2)->get_root());
+}
+
+void term_graph::internalize_lit(app* lit) {
+    if (is_internalized(lit)) return;
+
+    expr *e1, *e2;
+    if (m.is_eq (lit, e1, e2)) {
+        SASSERT(is_app(e1));
+        SASSERT(is_app(e2));
+        internalize_eq (::to_app(e1), ::to_app(e2));
+    }
+    else {
+        // NSB: this is thrown away.
+        // Is caller responsible for maintaining other predicates than equalities?
+        internalize_term(lit);
+    }
+}
+
+void term_graph::merge (term &t1, term &t2) {
+    SASSERT(t1.is_root());
+    SASSERT(t2.is_root());
+
+    if (&t1 == &t2) return;
+
+    term *a = &t1;
+    term *b = &t2;
+    if (a->get_class_size() > b->get_class_size()) {
+        std::swap(a, b);
+    }
+
+    // make 'a' be the root of the equivalence class of 'b'
+    b->set_root(*a);
+    for (term *it = &b->get_next(); it != b; it = &it->get_next()) {
+        it->set_root(*a);
+    }
+
+    // merge equivalence classes
+    a->merge_eq_class(*b);
+
+    // -- merge might have invalidated term2map cache
+    m_term2app.reset();
+    m_pinned.reset();
+}
+
+app* term_graph::mk_app_core (app *a) {
+    expr_ref_vector kids(m);
+    for (expr * arg : *a) {
+        kids.push_back (mk_app(::to_app(arg)));
+    }
+
+    app* res = m.mk_app(a->get_decl(), a->get_num_args(), kids.c_ptr());
+    m_pinned.push_back(res);
+
+    return res;
+}
+
+app_ref term_graph::mk_app(term const &r) {
+    SASSERT(r.is_root());
+
+    if (r.get_app()->get_num_args() == 0) {
+        return app_ref(r.get_app(), m);
+    }
+
+    app* res;
+    if (m_term2app.find(r.get_id(), res)) {
+        return app_ref(res, m);
+    }
+
+    res = mk_app_core (r.get_app());
+    m_term2app.insert(r.get_id(), res);
+    return app_ref(res, m);
+
+}
+app_ref term_graph::mk_app(app *a) {
+    term *t = get_term(a);
+    if (!t) 
+        return app_ref(a, m);
+    else 
+        return mk_app(t->get_root());
+
+}
+
+void term_graph::mk_equalities(term const &t, app_ref_vector &out) {
+    SASSERT(t.is_root());
+    app_ref rep(mk_app(t), m);
+
+    for (term *it = &t.get_next(); it != &t; it = &it->get_next()) {
+        app* mem = mk_app_core(it->get_app());
+        out.push_back (m.mk_eq (rep, mem));
+    }
+}
+
+void term_graph::mk_all_equalities(term const &t, app_ref_vector &out) {
+    mk_equalities(t, out);
+
+    for (term *it = &t.get_next(); it != &t; it = &it->get_next ()) {
+        app* a1 = mk_app_core (it->get_app());
+        for (term *it2 = &it->get_next(); it2 != &t; it2 = &it2->get_next()) {
+            app *a2;
+            a2 =  mk_app_core(it2->get_app());
+            out.push_back (m.mk_eq (a1, a2));
+        }
+    }
+}
+
+void term_graph::reset_marks() {
+    for (term * t : m_terms) {
+        t->set_mark(false);
+    }
+}
+
+/// Order of preference for roots of equivalence classes
+/// XXX This should be factored out to let clients control the preference
+bool term_graph::term_le(term const &t1, term const &t2) {
+
+    // prefer constants over applications
+    // prefer uninterpreted constants over values
+    // prefer smaller expressions over larger ones
+    app *a1, *a2;
+    a1 = t1.get_app();
+    a2 = t2.get_app();
+    if (a1->get_num_args() == 0 && a2->get_num_args() > 0) {
+        return true;
+    }
+    // NSB: how does this possibly define an order?
+    if (a1->get_num_args() == a2->get_num_args()) {
+        return m.is_value(a2);
+    }
+
+    unsigned sz1 = get_num_exprs(a1);
+    unsigned sz2 = get_num_exprs(a2);
+    return sz1 < sz2;
+}
+
+void term_graph::pick_root (term &t) {
+    term *r = &t;
+    for (term *it = &t.get_next(); it != &t; it = &it->get_next()) {
+        it->set_mark(true);
+        if (term_le(*it, *r)) { r = it; }
+    }
+
+    // -- if found something better, make it the new root
+    if (r != &t) {
+        r->mk_root();
+    }
+}
+/// Choose better roots for equivalence classes
+void term_graph::pick_roots() {
+    for (term* t : m_terms) {
+        if (!t->is_marked() && t->is_root()) 
+            pick_root(*t);
+    }
+    reset_marks();
+}
+
+void term_graph::display(std::ostream &out) {
+    for (term * t : m_terms) {
+        out << mk_pp(t->get_app(), m) << " is root " << t->is_root()
+            << " cls sz " << t->get_class_size()
+            << " term " << t
+            << "\n";
+    }
+}
+void term_graph::to_lits (app_ref_vector &lits, bool all_equalities) {
+    pick_roots();
+
+    for (app * a : m_lits) {
+        if (is_internalized(a)) {
+            lits.push_back (mk_app(a));
+        }
+    }
+
+    for (term * t : m_terms) {
+        if (!t->is_root()) 
+            continue;
+        else if (all_equalities) 
+            mk_all_equalities (*t, lits);         
+        else 
+            mk_equalities(*t, lits);
+    }
+}
+void term_graph::to_lits (expr_ref_vector &lits, bool all_equalities) {
+    app_ref_vector out(m);
+    to_lits (out, all_equalities);
+    for (app* a : out) {
+        lits.push_back(a);
+    }
+}
+
+app_ref term_graph::to_app() {
+    app_ref_vector lits(m);
+    to_lits(lits);
+    return mk_and(lits);
+}
+
+void term_graph::reset() {
+    m_term2app.reset();
+    m_pinned.reset();
+    m_app2term.reset();
+    std::for_each(m_terms.begin(), m_terms.end(), delete_proc<term>());
+    m_terms.reset();
+    m_lits.reset();
+}
+
+}
diff --git a/src/qe/qe_term_graph.h b/src/qe/qe_term_graph.h
new file mode 100644
index 000000000..76d793e59
--- /dev/null
+++ b/src/qe/qe_term_graph.h
@@ -0,0 +1,94 @@
+/**++
+Copyright (c) Arie Gurfinkel
+
+Module Name:
+
+    qe_term_graph.h
+
+Abstract:
+
+    Equivalence graph of terms
+
+Author:
+
+    Arie Gurfinkel
+
+Notes:
+
+--*/
+#ifndef QE_TERM_GRAPH_H__
+#define QE_TERM_GRAPH_H__
+
+#include "ast/ast.h"
+#include "util/plugin_manager.h"
+
+namespace qe {
+
+    class term;
+
+    class term_graph_plugin {
+        family_id m_id;
+    public:
+        term_graph_plugin(family_id fid) : m_id(fid) {}
+        virtual ~term_graph_plugin() {}
+
+        family_id get_family_id() const {return m_id;}
+        
+        /// Process (and potentially augment) a literal
+        virtual app_ref process_lit (app *lit) = 0;
+    };
+    
+    class term_graph {
+        ast_manager &m;
+        ptr_vector<term> m_terms;
+        app_ref_vector m_lits;
+        u_map<term* > m_app2term;
+        
+        app_ref_vector m_pinned;
+        u_map<app*> m_term2app;
+        
+        plugin_manager<term_graph_plugin> m_plugins;
+        
+        void merge(term &t1, term &t2);
+        
+        term *mk_term(app *t);
+        term *get_term(app *t);
+        
+        term *internalize_term(app *t);
+        void internalize_eq(app *a1, app *a2);
+        void internalize_lit(app *lit);
+        
+        bool is_internalized(app *a);
+        
+        bool term_le(term const &t1, term const &t2);
+        void pick_root (term &t);
+        void pick_roots();
+        
+        void reset_marks();
+        
+        app *mk_app_core(app* a);
+        app_ref mk_app(term const &t);
+        app_ref mk_app(app *a);
+        void mk_equalities(term const &t, app_ref_vector &out);
+        void mk_all_equalities(term const &t, app_ref_vector &out);
+        void display(std::ostream &out);
+    public:
+        term_graph(ast_manager &man);
+        ~term_graph();
+        
+        ast_manager &get_ast_manager() const { return m;}
+        
+        void add_lit(app *lit);
+        void add_lits(expr_ref_vector const &lits) {
+            for (expr* e : lits) add_lit(::to_app(e));
+        }
+        
+        void reset();
+        void to_lits(app_ref_vector &lits, bool all_equalities = false);
+        void to_lits(expr_ref_vector &lits, bool all_equalities = false);
+        app_ref to_app();
+        
+    };
+
+}
+#endif