diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index a26fcfe2c..b5d07ae1e 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -25,6 +25,8 @@ Notes:
 #include"automaton.h"
 #include"well_sorted.h"
 #include"var_subst.h"
+#include"symbolic_automata_def.h"
+
 
 expr_ref sym_expr::accept(expr* e) {
     ast_manager& m = m_t.get_manager();
@@ -37,6 +39,7 @@ expr_ref sym_expr::accept(expr* e) {
     }
     case t_char:
         SASSERT(m.get_sort(e) == m.get_sort(m_t));
+        SASSERT(m.get_sort(e) == m_sort);
         result = m.mk_eq(e, m_t);
         break;
     case t_range: {
@@ -67,8 +70,114 @@ struct display_expr1 {
     }
 };
 
+class sym_expr_boolean_algebra : public boolean_algebra<sym_expr*> {
+    ast_manager& m;
+    expr_solver& m_solver;
+    typedef sym_expr* T;
+public:
+    sym_expr_boolean_algebra(ast_manager& m, expr_solver& s): 
+        m(m), m_solver(s) {}
+
+    virtual T mk_false() {
+        expr_ref fml(m.mk_false(), m);
+        return sym_expr::mk_pred(fml, m.mk_bool_sort()); // use of Bool sort for bound variable is arbitrary
+    }
+    virtual T mk_true() {
+        expr_ref fml(m.mk_true(), m);
+        return sym_expr::mk_pred(fml, m.mk_bool_sort());
+    }
+    virtual T mk_and(T x, T y) {
+        if (x->is_char() && y->is_char()) {
+            if (x->get_char() == y->get_char()) {
+                return x;
+            }
+            if (m.are_distinct(x->get_char(), y->get_char())) {
+                expr_ref fml(m.mk_false(), m);
+                return sym_expr::mk_pred(fml, x->sort());
+            }
+        }
+        var_ref v(m.mk_var(0, x->sort()), m);
+        expr_ref fml1 = x->accept(v);
+        expr_ref fml2 = y->accept(v);
+        if (m.is_true(fml1)) return y;
+        if (m.is_true(fml2)) return x;
+        expr_ref fml(m.mk_and(fml1, fml2), m);
+        return sym_expr::mk_pred(fml, x->sort());
+    }
+    virtual T mk_or(T x, T y) {
+        if (x->is_char() && y->is_char() &&
+            x->get_char() == y->get_char()) {
+            return x;
+        }
+        var_ref v(m.mk_var(0, x->sort()), m);
+        expr_ref fml1 = x->accept(v);
+        expr_ref fml2 = y->accept(v);        
+        if (m.is_false(fml1)) return y;
+        if (m.is_false(fml2)) return x;
+        expr_ref fml(m.mk_or(fml1, fml2), m);
+        return sym_expr::mk_pred(fml, x->sort());
+    }
+
+    virtual T mk_and(unsigned sz, T const* ts) {
+        switch (sz) {
+        case 0: return mk_true();
+        case 1: return ts[0];
+        default: {
+            T t = ts[0];
+            for (unsigned i = 1; i < sz; ++i) {
+                t = mk_and(t, ts[i]);
+            }
+            return t;
+        }
+        }
+    }
+    virtual T mk_or(unsigned sz, T const* ts) {
+        switch (sz) {
+        case 0: return mk_false();
+        case 1: return ts[0];
+        default: {
+            T t = ts[0];
+            for (unsigned i = 1; i < sz; ++i) {
+                t = mk_or(t, ts[i]);
+            }
+            return t;
+        }
+        }
+    }
+    virtual lbool is_sat(T x) {
+        if (x->is_char()) {
+            return l_true;
+        }
+        if (x->is_range()) {
+            // TBD check lower is below upper.
+        }
+        expr_ref v(m.mk_fresh_const("x", x->sort()), m);
+        expr_ref fml = x->accept(v);
+        if (m.is_true(fml)) {
+            return l_true;
+        }
+        if (m.is_false(fml)) {
+            return l_false;
+        }
+        return m_solver.check_sat(fml);
+    }
+    virtual T mk_not(T x) {
+        var_ref v(m.mk_var(0, x->sort()), m);
+        expr_ref fml(m.mk_not(x->accept(v)), m);
+        return sym_expr::mk_pred(fml, x->sort());
+    }
+};
+
+re2automaton::re2automaton(ast_manager& m): m(m), u(m), bv(m), m_ba(0), m_sa(0) {}
+
+re2automaton::~re2automaton() {}
+
+void re2automaton::set_solver(expr_solver* solver) {
+    m_solver = solver;
+    m_ba = alloc(sym_expr_boolean_algebra, m, *solver);
+    m_sa = alloc(symbolic_automata_t, sm, *m_ba.get());
+}
 
-re2automaton::re2automaton(ast_manager& m): m(m), u(m), bv(m) {}
 
 eautomaton* re2automaton::operator()(expr* e) { 
     eautomaton* r = re2aut(e); 
@@ -136,7 +245,7 @@ eautomaton* re2automaton::re2aut(expr* e) {
             expr_ref _start(bv.mk_numeral(start, nb), m);
             expr_ref _stop(bv.mk_numeral(stop, nb), m);
             expr_ref _pred(m.mk_not(m.mk_and(bv.mk_ule(_start, v), bv.mk_ule(v, _stop))), m);
-            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred));
+            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred, s));
             return a.detach();
         }
         else if (u.re.is_to_re(e0, e1) && u.str.is_string(e1, s1) && s1.length() == 1) {
@@ -145,13 +254,14 @@ eautomaton* re2automaton::re2aut(expr* e) {
             expr_ref v(m.mk_var(0, s), m);
             expr_ref _ch(bv.mk_numeral(s1[0], nb), m);          
             expr_ref _pred(m.mk_not(m.mk_eq(v, _ch)), m);
-            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred));
+            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred, s));
             return a.detach();
         }
         else if (u.re.is_to_re(e0, e1) && u.str.is_unit(e1, e2)) {
-            expr_ref v(m.mk_var(0, m.get_sort(e2)), m);
+            sort* s = m.get_sort(e2);
+            expr_ref v(m.mk_var(0, s), m);
             expr_ref _pred(m.mk_not(m.mk_eq(v, e2)), m);
-            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred));
+            a = alloc(eautomaton, sm, sym_expr::mk_pred(_pred, s));
             return a.detach();
         }
         else {
@@ -187,14 +297,15 @@ eautomaton* re2automaton::re2aut(expr* e) {
     }
     else if (u.re.is_full(e)) {
         expr_ref tt(m.mk_true(), m);
-        sym_expr* _true = sym_expr::mk_pred(tt);
+        sort* seq_s, *char_s;
+        VERIFY (u.is_re(m.get_sort(e), seq_s));
+        VERIFY (u.is_seq(seq_s, char_s));
+        sym_expr* _true = sym_expr::mk_pred(tt, char_s);
         return eautomaton::mk_loop(sm, _true);
     }
-#if 0
-    else if (u.re.is_intersect(e, e1, e2)) {
-        // maybe later
+    else if (u.re.is_intersection(e, e1, e2) && m_sa && (a = re2aut(e1)) && (b = re2aut(e2))) {
+        return m_sa->mk_product(*a, *b);
     }
-#endif
     
     return 0;
 }
diff --git a/src/ast/rewriter/seq_rewriter.h b/src/ast/rewriter/seq_rewriter.h
index 83dd8f653..718658652 100644
--- a/src/ast/rewriter/seq_rewriter.h
+++ b/src/ast/rewriter/seq_rewriter.h
@@ -25,6 +25,7 @@ Notes:
 #include"params.h"
 #include"lbool.h"
 #include"automaton.h"
+#include"symbolic_automata.h"
 
 class sym_expr {
     enum ty {
@@ -33,21 +34,24 @@ class sym_expr {
         t_range
     };
     ty       m_ty;
+    sort*    m_sort;
     expr_ref m_t;
     expr_ref m_s;
     unsigned m_ref;
-    sym_expr(ty ty, expr_ref& t, expr_ref& s) : m_ty(ty), m_t(t), m_s(s), m_ref(0) {}
+    sym_expr(ty ty, expr_ref& t, expr_ref& s, sort* srt) : m_ty(ty), m_sort(srt), m_t(t), m_s(s), m_ref(0) {}
 public:
     expr_ref accept(expr* e);
-    static sym_expr* mk_char(expr_ref& t) { return alloc(sym_expr, t_char, t, t); }
+    static sym_expr* mk_char(expr_ref& t) { return alloc(sym_expr, t_char, t, t, t.get_manager().get_sort(t)); }
     static sym_expr* mk_char(ast_manager& m, expr* t) { expr_ref tr(t, m); return mk_char(tr); }
-    static sym_expr* mk_pred(expr_ref& t) { return alloc(sym_expr, t_pred, t, t); }
-    static sym_expr* mk_range(expr_ref& lo, expr_ref& hi) { return alloc(sym_expr, t_range, lo, hi); }
+    static sym_expr* mk_pred(expr_ref& t, sort* s) { return alloc(sym_expr, t_pred, t, t, s); }
+    static sym_expr* mk_range(expr_ref& lo, expr_ref& hi) { return alloc(sym_expr, t_range, lo, hi, lo.get_manager().get_sort(hi)); }
     void inc_ref() { ++m_ref;  }
     void dec_ref() { --m_ref; if (m_ref == 0) dealloc(this); }
     std::ostream& display(std::ostream& out) const;
     bool is_char() const { return m_ty == t_char; }
     bool is_pred() const { return !is_char(); }
+    bool is_range() const { return m_ty == t_range; }
+    sort* sort() const { return m_sort; }
     expr* get_char() const { SASSERT(is_char()); return m_t; }
 
 };
@@ -58,17 +62,31 @@ public:
     void dec_ref(sym_expr* s) { if (s) s->dec_ref(); }
 };
 
+class expr_solver {
+public:
+    virtual ~expr_solver() {}
+    virtual lbool check_sat(expr* e) = 0;
+};
+
 typedef automaton<sym_expr, sym_expr_manager> eautomaton;
 class re2automaton {
+    typedef boolean_algebra<sym_expr*> boolean_algebra_t;
+    typedef symbolic_automata<sym_expr, sym_expr_manager> symbolic_automata_t;
     ast_manager& m;
     sym_expr_manager sm;
     seq_util     u;     
     bv_util      bv;
+    scoped_ptr<expr_solver>         m_solver;
+    scoped_ptr<boolean_algebra_t>   m_ba;
+    scoped_ptr<symbolic_automata_t> m_sa;
+
     eautomaton* re2aut(expr* e);
     eautomaton* seq2aut(expr* e);
- public:
+public:
     re2automaton(ast_manager& m);
+    ~re2automaton();
     eautomaton* operator()(expr* e);
+    void set_solver(expr_solver* solver);
 };
 
 /**
diff --git a/src/math/automata/automaton.h b/src/math/automata/automaton.h
index 54c969bbb..dd1ff87f5 100644
--- a/src/math/automata/automaton.h
+++ b/src/math/automata/automaton.h
@@ -178,15 +178,19 @@ public:
         return alloc(automaton, a.m, a.init(), final, mvs);
     }
 
+    automaton* clone() const {
+        return clone(*this);
+    }
+
     // create the sum of disjoint automata
     static automaton* mk_union(automaton const& a, automaton const& b) {
         SASSERT(&a.m == &b.m);
         M& m = a.m;
         if (a.is_empty()) {
-            return clone(b);
+            return b.clone();
         }
         if (b.is_empty()) {
-            return clone(a);
+            return a.clone();
         }
         moves mvs;
         unsigned_vector final;
@@ -213,7 +217,7 @@ public:
             mvs.push_back(move(m, 0, a.init() + offset));
         }
         if (a.is_empty()) {
-            return clone(a);
+            return a.clone();
         }
 
         mvs.push_back(move(m, init, a.final_state() + offset));
@@ -227,16 +231,16 @@ public:
         SASSERT(&a.m == &b.m);
         M& m = a.m;
         if (a.is_empty()) {
-            return clone(a);
+            return a.clone();
         }
         if (b.is_empty()) {
-            return clone(b);
+            return b.clone();
         }
         if (a.is_epsilon()) {
-            return clone(b);
+            return b.clone();
         }
         if (b.is_epsilon()) {
-            return clone(a);
+            return a.clone();
         }
 
         moves mvs;
@@ -458,6 +462,7 @@ public:
     }
 
     unsigned init() const { return m_init; }
+    unsigned_vector const& final_states() const { return m_final_states; }
     unsigned in_degree(unsigned state) const { return m_delta_inv[state].size(); }
     unsigned out_degree(unsigned state) const { return m_delta[state].size(); }
     move const& get_move_from(unsigned state) const { SASSERT(m_delta[state].size() == 1); return m_delta[state][0]; }
diff --git a/src/math/automata/boolean_algebra.h b/src/math/automata/boolean_algebra.h
new file mode 100644
index 000000000..503878ef3
--- /dev/null
+++ b/src/math/automata/boolean_algebra.h
@@ -0,0 +1,46 @@
+/*++
+Copyright (c) 2015 Microsoft Corporation
+
+Module Name:
+
+    boolean_algebra.h
+
+Abstract:
+
+    Boolean Algebra, a la Margus Veanes Automata library.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2016-2-27
+
+Revision History:
+
+
+--*/
+
+#ifndef BOOLEAN_ALGEBRA_H_
+#define BOOLEAN_ALGEBRA_H_
+
+#include "util.h"
+
+template<class T>
+class positive_boolean_algebra {
+public:
+    virtual T mk_false() = 0;
+    virtual T mk_true() = 0;
+    virtual T mk_and(T x, T y) = 0;
+    virtual T mk_or(T x, T y) = 0;
+    virtual T mk_and(unsigned sz, T const* ts) = 0;
+    virtual T mk_or(unsigned sz, T const* ts) = 0;
+    virtual lbool is_sat(T x) = 0;
+};
+
+template<class T>
+class boolean_algebra : public positive_boolean_algebra<T> {
+public:
+    virtual T mk_not(T x) = 0;
+    //virtual lbool are_equivalent(T x, T y) = 0;
+    //virtual T simplify(T x) = 0;    
+};
+
+#endif
diff --git a/src/math/automata/symbolic_automata.h b/src/math/automata/symbolic_automata.h
new file mode 100644
index 000000000..d77e0548d
--- /dev/null
+++ b/src/math/automata/symbolic_automata.h
@@ -0,0 +1,104 @@
+/*++
+Copyright (c) 2015 Microsoft Corporation
+
+Module Name:
+
+    symbolic_automata.h
+
+Abstract:
+
+    Symbolic Automata over Boolean Algebras, a la Margus Veanes Automata library.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2016-02-27.
+
+Revision History:
+
+
+--*/
+
+#ifndef SYMBOLIC_AUTOMATA_H_
+#define SYMBOLIC_AUTOMATA_H_
+
+
+#include "automaton.h"
+#include "boolean_algebra.h"
+
+
+template<class T, class M = default_value_manager<T> >
+class symbolic_automata {
+    typedef automaton<T, M>    automaton_t;
+    typedef boolean_algebra<T*> ba_t;
+    typedef typename automaton_t::move  move_t;
+    typedef vector<move_t>     moves_t;
+    typedef obj_ref<T, M>      ref_t;
+    typedef ref_vector<T, M>   refs_t;
+
+    M&    m;
+    ba_t& m_ba;
+
+
+    class block {
+        uint_set m_set;
+        unsigned m_rep;
+        bool     m_rep_chosen;
+    public:
+
+        block(): m_rep(0), m_rep_chosen(false) {}
+
+        block(uint_set const& s):
+            m_set(s),
+            m_rep(0),
+            m_rep_chosen(false) {
+        }
+
+        block(unsigned_vector const& vs) {
+            for (unsigned i = 0; i < vs.size(); ++i) {
+                m_set.insert(vs[i]);               
+            }
+            m_rep_chosen = false;
+            m_rep = 0;
+        }
+
+        block& operator=(block const& b) {
+            m_set = b.m_set;
+            m_rep = 0;
+            m_rep_chosen = false;
+            return *this;
+        }
+
+        unsigned get_representative() {
+            if (!m_rep_chosen) {
+                uint_set::iterator it = m_set.begin();
+                if (m_set.end() != it) {
+                    m_rep = *it;                    
+                }
+                m_rep_chosen = true;
+            }
+            return m_rep;
+        }
+
+        void add(unsigned i) { m_set.insert(i); }
+        bool contains(unsigned i) const { return m_set.contains(i); }        
+        bool is_empty() const { return m_set.empty(); }
+        unsigned size() const { return m_set.num_elems(); }
+        void remove(unsigned i) { m_set.remove(i); m_rep_chosen = false; }        
+        void clear() { m_set.reset(); m_rep_chosen = false; }
+        uint_set::iterator begin() { return m_set.begin(); }
+        uint_set::iterator end() { return m_set.end(); }
+    };
+
+public:
+    symbolic_automata(M& m, ba_t& ba): m(m), m_ba(ba) {}
+    automaton_t* mk_determinstic(automaton_t& a);
+    automaton_t* mk_complement(automaton_t& a);
+    automaton_t* remove_epsilons(automaton_t& a);
+    automaton_t* mk_total(automaton_t& a);
+    automaton_t* mk_minimize(automaton_t& a);
+    automaton_t* mk_product(automaton_t& a, automaton_t& b);
+};
+
+
+
+#endif 
diff --git a/src/math/automata/symbolic_automata_def.h b/src/math/automata/symbolic_automata_def.h
new file mode 100644
index 000000000..90dd98d10
--- /dev/null
+++ b/src/math/automata/symbolic_automata_def.h
@@ -0,0 +1,227 @@
+/*++
+Copyright (c) 2015 Microsoft Corporation
+
+Module Name:
+
+    symbolic_automata_def.h
+
+Abstract:
+
+    Symbolic Automata over Boolean Algebras, a la Margus Veanes Automata library.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2016-02-27.
+
+Revision History:
+
+
+--*/
+
+#ifndef SYMBOLIC_AUTOMATA_DEF_H_
+#define SYMBOLIC_AUTOMATA_DEF_H_
+
+
+#include "symbolic_automata.h"
+#include "hashtable.h"
+
+typedef std::pair<unsigned, unsigned> unsigned_pair;
+
+
+
+template<class T, class M>
+typename symbolic_automata<T, M>::automaton_t* symbolic_automata<T, M>::mk_total(automaton_t& a) {
+    unsigned dead_state = a.num_states();
+    moves_t mvs;
+    for (unsigned i = 0; i < dead_state; ++i) {
+        mvs.reset();
+        a.get_moves(i, mvs, true);
+        refs_t vs(m);
+        
+        for (unsigned j = 0; j < mvs.size(); ++j) {
+            mv.push_back(mvs[j]());
+        }
+        ref_t cond(m_ba.mk_not(m_ba.mk_or(vs.size(), vs.c_ptr())), m);
+        lbool is_sat = m_ba.is_sat(cond);
+        if (is_sat == l_undef) {
+            return 0;
+        }
+        if (is_sat == l_true) {
+            new_mvs.push_back(move_t(m, i, dead_state, cond));
+        }
+    }
+    if (new_mvs.empty()) {
+        return a.clone();
+    }
+    new_mvs.push_back(move_t(m, dead_state, dead_state, m_ba.mk_true()));
+    automaton_t::append_moves(0, a, new_mvs);
+    
+    return alloc(automaton_t, m, a.init(), a.final_states(), new_mvs);        
+}
+
+template<class T, class M>
+typename symbolic_automata<T, M>::automaton_t* symbolic_automata<T, M>::mk_minimize(automaton_t& a) {
+    if (a.is_empty()) {
+        return a.clone();
+    }
+    if (a.is_epsilon()) {
+        return a.clone();
+    }
+    // SASSERT(a.is_deterministic());
+    
+    scoped_ptr<automaton_t> fa = mk_total(a);
+    if (!fa) {
+        return 0;
+    }
+    
+    block final_block(fa->final_states());
+    block non_final_block(fa->non_final_states());
+    vector<block> blocks;
+    for (unsigned i = 0; i < fa->num_states(); ++i) {
+        if (fa->is_final_state(i)) {
+            blocks.push_back(final_block);
+        }
+        else {
+            blocks.push_back(non_final_block);
+        }
+    }
+    vector<block> W;
+    if (final_block.size() > non_final_block.size()) {
+        W.push_back(non_final_block);
+    }
+    else {
+        W.push_back(final_block);
+    }
+    
+#if 0
+    
+    refs_t trail(m);
+    u_map<T*> gamma;
+    moves_t mvs;
+    while (!W.empty()) {
+        block R(W.back());
+        W.pop_back();
+        block Rcopy(R);
+        gamma.reset();
+        uint_set::iterator it = Rcopy.begin(), end = Rcopy.end();
+        for (; it != end; ++it) {
+            unsigned q = *it;
+            mvs.reset();
+            fa->get_moves_to(q, mvs);
+            for (unsigned i = 0; i < mvs.size(); ++i) {
+                unsigned src = mvs[i].src();
+                if (blocks[src].size() > 1) {
+                    T* t = mvs[i]();
+                    if (gamma.find(src, t1)) {
+                        t = m_ba.mk_or(t, t1);
+                        trail.push_back(t);
+                    }
+                    gamma.insert(src, t);
+                }
+            }
+        }
+        hashtable<block*> relevant;
+        u_map<T*>::iterator end = gamma.end();
+        for (u_map<T*>::iterator it = gamma.begin(); it != end; ++it) {
+            relevant.insert(blocks[it->m_key]);
+        }
+        
+    }
+#endif
+    
+    return 0;
+        
+}
+
+template<class T, class M>
+typename symbolic_automata<T, M>::automaton_t* symbolic_automata<T, M>::mk_product(automaton_t& a, automaton_t& b) {
+    map<unsigned_pair, unsigned, pair_hash<unsigned_hash, unsigned_hash>, default_eq<unsigned_pair> > state_ids;
+    unsigned_pair init_pair(a.init(), b.init());
+    svector<unsigned_pair> todo;
+    todo.push_back(init_pair);
+    state_ids.insert(init_pair, 0);
+    moves_t mvs;
+    unsigned_vector final;
+    if (a.is_final_state(a.init()) && b.is_final_state(b.init())) {
+        final.push_back(0);
+    }
+    unsigned n = 1;
+    moves_t mvsA, mvsB;
+    while (!todo.empty()) {
+        unsigned_pair curr_pair = todo.back();
+        todo.pop_back();
+        unsigned src = state_ids[curr_pair];
+        mvsA.reset(); mvsB.reset();
+        a.get_moves_from(curr_pair.first,  mvsA, true);
+        b.get_moves_from(curr_pair.second, mvsB, true);
+        for (unsigned i = 0; i < mvsA.size(); ++i) {
+            for (unsigned j = 0; j < mvsB.size(); ++j) {
+                ref_t ab(m_ba.mk_and(mvsA[i].t(), mvsB[j].t()), m);   
+                lbool is_sat = m_ba.is_sat(ab);
+                if (is_sat == l_false) {
+                    continue;
+                }
+                else if (is_sat == l_undef) {
+                    return 0;
+                }
+                unsigned_pair tgt_pair(mvsA[i].dst(), mvsB[j].dst());
+                unsigned tgt;
+                if (!state_ids.find(tgt_pair, tgt)) {
+                    tgt = n++;
+                    state_ids.insert(tgt_pair, tgt);
+                    todo.push_back(tgt_pair);
+                    if (a.is_final_state(tgt_pair.first) && b.is_final_state(tgt_pair.second)) {
+                        final.push_back(tgt);
+                    }
+                }
+                mvs.push_back(move_t(m, src, tgt, ab));
+            }
+        }
+    }
+    
+    if (final.empty()) {
+        return alloc(automaton_t, m);
+    }
+    vector<moves_t> inv(n, moves_t());
+    for (unsigned i = 0; i < mvs.size(); ++i) {
+        move_t const& mv = mvs[i];
+        inv[mv.dst()].push_back(move_t(m, mv.dst(), mv.src(), mv.t())); 
+    }
+    
+    svector<bool> back_reachable(n, false);
+    for (unsigned i = 0; i < final.size(); ++i) {
+        back_reachable[final[i]] = true;
+    }
+    
+    unsigned_vector stack(final);
+    while (!stack.empty()) {
+        unsigned state = stack.back();
+        stack.pop_back();
+        moves_t const& mv = inv[state];
+        for (unsigned i = 0; i < mv.size(); ++i) {
+            state = mv[i].dst();
+            if (!back_reachable[state]) {
+                back_reachable[state] = true;
+                stack.push_back(state);
+            }
+        }
+    }
+    
+    moves_t mvs1;
+    for (unsigned i = 0; i < mvs.size(); ++i) {
+        move_t const& mv = mvs[i];
+        if (back_reachable[mv.dst()]) {
+            mvs1.push_back(mv);
+        }
+    }
+    if (mvs1.empty()) {
+        return alloc(automaton_t, m);
+    }
+    else {
+        return alloc(automaton_t, m, 0, final, mvs1);
+    }
+} 
+
+
+
+#endif 
diff --git a/src/smt/theory_seq.cpp b/src/smt/theory_seq.cpp
index c3c8a004c..551e80c85 100644
--- a/src/smt/theory_seq.cpp
+++ b/src/smt/theory_seq.cpp
@@ -25,6 +25,7 @@ Revision History:
 #include "theory_seq.h"
 #include "ast_trail.h"
 #include "theory_arith.h"
+#include "smt_kernel.h"
 
 using namespace smt;
 
@@ -36,6 +37,21 @@ struct display_expr {
     }
 };
 
+class seq_expr_solver : public expr_solver {
+    kernel m_kernel;
+public:
+    seq_expr_solver(ast_manager& m, smt_params& fp):
+        m_kernel(m, fp)
+    {}
+
+    virtual lbool check_sat(expr* e) {
+        m_kernel.push();
+        m_kernel.assert_expr(e);
+        lbool r = m_kernel.check();
+        m_kernel.pop(1);
+        return r;
+    }
+};
 
 
 void theory_seq::solution_map::update(expr* e, expr* r, dependency* d) {
@@ -199,26 +215,31 @@ theory_seq::theory_seq(ast_manager& m):
     m_new_solution(false),
     m_new_propagation(false),
     m_mk_aut(m) {
-    m_prefix = "seq.prefix.suffix";
-    m_suffix = "seq.suffix.prefix";
-    m_accept = "aut.accept";
-    m_reject = "aut.reject";
+    m_prefix         = "seq.p.suffix";
+    m_suffix         = "seq.s.prefix";
+    m_accept         = "aut.accept";
+    m_reject         = "aut.reject";
     m_tail           = "seq.tail";
     m_nth            = "seq.nth";
     m_seq_first      = "seq.first";
     m_seq_last       = "seq.last";
-    m_indexof_left   = "seq.indexof.left";
-    m_indexof_right  = "seq.indexof.right";
+    m_indexof_left   = "seq.idx.left";
+    m_indexof_right  = "seq.idx.right";
     m_aut_step       = "aut.step";
     m_pre            = "seq.pre";  // (seq.pre s l):  prefix of string s of length l
     m_post           = "seq.post"; // (seq.post s l): suffix of string s of length l
     m_eq             = "seq.eq";
+
 }
 
 theory_seq::~theory_seq() {
     m_trail_stack.reset();
 }
 
+void theory_seq::init(context* ctx) {
+    theory::init(ctx);
+    m_mk_aut.set_solver(alloc(seq_expr_solver, m, get_context().get_fparams()));
+}
 
 final_check_status theory_seq::final_check_eh() {
     TRACE("seq", display(tout << "level: " << get_context().get_scope_level() << "\n"););
diff --git a/src/smt/theory_seq.h b/src/smt/theory_seq.h
index 2d6631387..8206eeca4 100644
--- a/src/smt/theory_seq.h
+++ b/src/smt/theory_seq.h
@@ -332,6 +332,7 @@ namespace smt {
 
         obj_hashtable<expr>            m_fixed;            // string variables that are fixed length.
 
+        virtual void init(context* ctx);
         virtual final_check_status final_check_eh();
         virtual bool internalize_atom(app* atom, bool) { return internalize_term(atom); }
         virtual bool internalize_term(app*);