diff --git a/scripts/mk_project.py b/scripts/mk_project.py
index 9ceec29eb..f9f752a18 100644
--- a/scripts/mk_project.py
+++ b/scripts/mk_project.py
@@ -66,7 +66,7 @@ def init_project_def():
     add_lib('clp', ['muz', 'transforms'], 'muz/clp')
     add_lib('tab', ['muz', 'transforms'], 'muz/tab')
     add_lib('bmc', ['muz', 'transforms'], 'muz/bmc')
-    add_lib('ddnf', ['muz', 'transforms'], 'muz/ddnf')
+    add_lib('ddnf', ['muz', 'transforms', 'rel'], 'muz/ddnf')
     add_lib('duality_intf', ['muz', 'transforms', 'duality'], 'muz/duality')
     add_lib('fp',  ['muz', 'pdr', 'clp', 'tab', 'rel', 'bmc', 'duality_intf', 'ddnf'], 'muz/fp')
     add_lib('smtlogic_tactics', ['arith_tactics', 'bv_tactics', 'nlsat_tactic', 'smt_tactic', 'aig_tactic', 'fp', 'muz','qe'], 'tactic/smtlogics')
diff --git a/src/ast/substitution/substitution_tree.cpp b/src/ast/substitution/substitution_tree.cpp
index 037d51e32..6aaa2da66 100644
--- a/src/ast/substitution/substitution_tree.cpp
+++ b/src/ast/substitution/substitution_tree.cpp
@@ -793,8 +793,10 @@ bool substitution_tree::visit(expr * e, st_visitor & st, node * r) {
                 }
                 else {
                     TRACE("st_bug", tout << "found match:\n"; m_subst->display(tout); tout << "m_subst: " << m_subst << "\n";);
-                    if (!st(n->m_expr))
+                    if (!st(n->m_expr)) {
+                        clear_stack();
                         return false;
+                    }
                     if (!backtrack())
                         break;
                 }
@@ -806,12 +808,16 @@ bool substitution_tree::visit(expr * e, st_visitor & st, node * r) {
         else if (!backtrack())
             break;
     }
+    clear_stack();
+    return true;
+}
+
+void substitution_tree::clear_stack() {
     while (!m_bstack.empty()) {
         m_subst->pop_scope();
         m_bstack.pop_back();
     }
     m_subst->pop_scope();
-    return true;
 }
 
 template<substitution_tree::st_visit_mode Mode>
diff --git a/src/ast/substitution/substitution_tree.h b/src/ast/substitution/substitution_tree.h
index caa3d37cb..07723a8e4 100644
--- a/src/ast/substitution/substitution_tree.h
+++ b/src/ast/substitution/substitution_tree.h
@@ -123,6 +123,8 @@ class substitution_tree {
     template<st_visit_mode Mode>
     void visit(expr * e, st_visitor & st, unsigned in_offset, unsigned st_offset, unsigned reg_offset);
 
+    void clear_stack();
+
 public:
     substitution_tree(ast_manager & m);
     ~substitution_tree();
diff --git a/src/muz/ddnf/doc.cpp b/src/muz/ddnf/doc.cpp
new file mode 100644
index 000000000..8690e8218
--- /dev/null
+++ b/src/muz/ddnf/doc.cpp
@@ -0,0 +1,82 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    doc.cpp
+
+Abstract:
+
+    difference of cubes.
+
+Author:
+
+    Nuno Lopes (a-nlopes) 2013-03-01
+    Nikolaj Bjorner (nbjorner) 2014-09-15
+
+Revision History:
+
+    Based on ternary_diff_bitvector by Nuno Lopes.
+
+--*/
+
+#include "doc.h"
+void doc_manager::reset() {
+}
+doc* doc_manager::allocate() {
+    return 0;
+}
+doc* doc_manager::allocate1() {
+    return 0;
+}
+doc* doc_manager::allocate0() {
+    return 0;                                                
+}
+doc* doc_manager::allocateX() {
+    return 0;
+}
+doc* doc_manager::allocate(doc const& src) {
+    return 0;
+}
+doc* doc_manager::allocate(uint64 n) {
+    return 0;
+}
+doc* doc_manager::allocate(rational const& r) {
+    return 0;
+}
+doc* doc_manager::allocate(uint64 n, unsigned hi, unsigned lo) {
+    return 0;
+}
+void doc_manager::deallocate(doc* src) {
+}
+void doc_manager::copy(doc& dst, doc const& src) const {
+}
+doc& doc_manager::fill0(doc& src) const {
+    return src;
+}
+doc& doc_manager::fill1(doc& src) const {
+    return src;
+}
+doc& doc_manager::fillX(doc& src) const {
+    return src;
+}
+bool doc_manager::set_and(doc& dst, doc const& src) const {
+    return false;
+}
+void doc_manager::complement(doc const& src, ptr_vector<doc>& result) {
+}
+void doc_manager::subtract(doc const& A, doc const& B, ptr_vector<doc>& result) {
+}
+bool doc_manager::equals(doc const& a, doc const& b) const {
+    return false;
+}
+unsigned doc_manager::hash(doc const& src) const {
+    return 0;
+}
+bool doc_manager::contains(doc const& a, doc const& b) const {
+    return false;
+}
+std::ostream& doc_manager::display(std::ostream& out, doc const& b) const {
+    return out;
+}
+
diff --git a/src/muz/ddnf/doc.h b/src/muz/ddnf/doc.h
index 641e9513c..aa32fd47a 100644
--- a/src/muz/ddnf/doc.h
+++ b/src/muz/ddnf/doc.h
@@ -11,6 +11,7 @@ Abstract:
 
 Author:
 
+    Nuno Lopes (a-nlopes) 2013-03-01
     Nikolaj Bjorner (nbjorner) 2014-09-15
 
 Revision History:
@@ -22,8 +23,6 @@ Revision History:
 #ifndef _DOC_H_
 #define _DOC_H_
 
-#if 0
-
 #include "tbv.h"
 
 class doc;
@@ -50,27 +49,38 @@ public:
     doc& fill1(doc& src) const;
     doc& fillX(doc& src) const;
     bool set_and(doc& dst, doc const& src) const;
-    //  doc& set_or(doc& dst,  doc const& src) const;
-    void neg(doc const& src, union_bvec<doc_mananger, doc>& result) const;
+    void complement(doc const& src, ptr_vector<doc>& result);
+    void subtract(doc const& A, doc const& B, ptr_vector<doc>& result);
     bool equals(doc const& a, doc const& b) const;
     unsigned hash(doc const& src) const;
     bool contains(doc const& a, doc const& b) const;
     std::ostream& display(std::ostream& out, doc const& b) const;
+    unsigned num_tbits() const { return m.num_tbits(); }
 };
 
 // union of tbv*, union of doc*
 template<typename M, typename T>
-class union_bvec {
+class union_bvec { 
     ptr_vector<T> m_elems; // TBD: reuse allocator of M
 public:
     unsigned size() const { return m_elems.size(); }
     T& operator[](unsigned idx) const { return *m_elems[idx]; }
+    bool empty() const { return m_elems.empty(); }    
+    bool contains(M& m, T& t) const {
+        for (unsigned i = 0; i < m_elems.size(); ++i) {
+            if (m.contains(*m_elems[i], t)) return true;
+        }
+        return false;
+    }
+    void push_back(T* t) {
+        m_elems.push_back(t);
+    }
     void reset(M& m) {
         for (unsigned i = 0; i < m_elems.size(); ++i) {
             m.deallocate(m_elems[i]);
         }
         m_elems.reset(); 
-    }
+    }    
     void insert(M& m, T* t) {
         unsigned sz = size(), j = 0;
         bool found = false;
@@ -102,13 +112,13 @@ public:
         }
         return true;
     }
-    void insert(M& m, union_set const& other) {
+    void insert(M& m, union_bvec const& other) {
         for (unsigned i = 0; i < other.size(); ++i) {
             insert(m, other[i]);
         }
     }
-    void intersect(M& m, union_set const& other, union_set& result) {
-        result.reset(m);
+    void intersect(M& m, union_bvec const& other) {
+        union_bvec result;
         unsigned sz1 = size();
         unsigned sz2 = other.size();
         T* inter = m.allocate();
@@ -121,29 +131,30 @@ public:
             }
         }
         m.deallocate(inter);
+        std::swap(result, *this);
+        result.reset();
     }
-    void neg(M& m, union_set& result) {     
-        union_set negated;
+    void complement(M& m, union_bvec& result) {     
+        union_bvec negated;
         result.reset(m);
         result.push_back(m.allocateX());
         unsigned sz = size();
-        for (unsigned i = 0; !result.empty() && i < sz; ++i) {
-            // m.set_neg(*m_elems[i]);
-            // result.intersect(m, negated);
+        for (unsigned i = 0; !empty() && i < sz; ++i) {
+            m.complement(*m_elems[i], negated.m_elems);
+            result.intersect(m, negated);
+            negated.reset(m);
         }
     }
 
-    void subtract(M& m, union_set const& other, union_set& result) {
-        result.reset(m);
-        
-    }
 };
 
+typedef union_bvec<tbv_manager, tbv> utbv;
+
 class doc {
     // pos \ (neg_0 \/ ... \/ neg_n)
     friend class doc_manager;
     tbv*                         m_pos;
-    union_bvec<tbv_manager, tbv> m_neg;
+    utbv                         m_neg;
 public:
 
     struct eq {
@@ -161,55 +172,31 @@ public:
             return m.hash(d);
         }
     };
+
+    tbv& pos() { return *m_pos; }
+    utbv& neg() { return m_neg; }
+    tbv const& pos() const { return *m_pos; }
+    utbv const& neg() const { return m_neg; }
         
 };
 
-#endif
+typedef union_bvec<doc_manager, doc> udoc;
+
+class doc_ref {
+    doc_manager& dm;
+    doc* d;
+public:
+    doc_ref(doc_manager& dm):dm(dm),d(0) {}
+    doc_ref(doc_manager& dm, doc* d):dm(dm),d(d) {}
+    ~doc_ref() {
+        if (d) dm.deallocate(d);
+    }
+    doc_ref& operator=(doc* d2) {
+        if (d) dm.deallocate(d);
+        d = d2;
+    }
+    doc& operator*() { return *d; }
+};
 
 #endif /* _DOC_H_ */
 
-#if 0
-
-    class utbv {
-        friend class ternary_bitvector;
-
-        ternary_bitvector m_pos;
-        union_ternary_bitvector<ternary_bitvector> m_neg;
-
-    public:
-        utbv() : m_pos(), m_neg(0) {}
-        utbv(unsigned size) : m_pos(size), m_neg(size) {}
-        utbv(unsigned size, bool full);
-        utbv(const rational& n, unsigned num_bits);
-        explicit utbv(const ternary_bitvector & tbv);
-
-        bool contains(const utbv & other) const;
-        bool contains(const ternary_bitvector & other) const;
-        bool contains(unsigned offset, const utbv& other,
-                      unsigned other_offset, unsigned length) const;
-        bool is_empty() const;
-
-        utbv band(const utbv& other) const;
-        void neg(union_ternary_bitvector<utbv>& result) const;
-
-        static bool has_subtract() { return true; }
-        void subtract(const union_ternary_bitvector<utbv>& other,
-            union_ternary_bitvector<utbv>& result) const;
-
-
-        unsigned get(unsigned idx);
-        void set(unsigned idx, unsigned val);
-
-        void swap(utbv & other);
-        void reset();
-
-
-        void display(std::ostream & out) const;
-
-    private:
-        void add_negated(const ternary_bitvector& neg);
-        void add_negated(const union_ternary_bitvector<ternary_bitvector>& neg);
-        bool fold_neg();
-    };
-
-#endif
diff --git a/src/muz/ddnf/tbv.cpp b/src/muz/ddnf/tbv.cpp
index 71bc8dc44..b6b5e1b6d 100644
--- a/src/muz/ddnf/tbv.cpp
+++ b/src/muz/ddnf/tbv.cpp
@@ -60,11 +60,33 @@ tbv* tbv_manager::allocate(uint64 val) {
 tbv* tbv_manager::allocate(uint64 val, unsigned hi, unsigned lo) {
     tbv* v = allocateX();
     SASSERT(64 >= m.num_bits() && m.num_bits() > hi && hi >= lo);
-    for (unsigned i = 0; i < hi - lo + 1; ++i) {
-        v->set(lo + i, (val & (1ULL << i))?BIT_1:BIT_0);
-    }
+    v->set(val, hi, lo);
     return v;
 }
+void tbv::set(uint64 val, unsigned hi, unsigned lo) {
+    for (unsigned i = 0; i < hi - lo + 1; ++i) {
+        set(lo + i, (val & (1ULL << i))?BIT_1:BIT_0);
+    }
+}
+void tbv::set(rational const& r, unsigned hi, unsigned lo) {
+    if (r.is_uint64()) {
+        set(r.get_uint64(), hi, lo);
+        return;
+    }
+    for (unsigned i = 0; i < hi - lo + 1; ++i) {
+        if (bitwise_and(r, rational::power_of_two(i)).is_zero())
+            set(lo + i, BIT_0);
+        else
+            set(lo + i, BIT_1);
+    }
+}
+
+void tbv::set(tbv const& other, unsigned hi, unsigned lo) {
+    for (unsigned i = 0; i < hi - lo + 1; ++i) {
+        set(lo + i, other.get(i));
+    }
+}
+
 
 tbv* tbv_manager::allocate(rational const& r) {
     if (r.is_uint64()) {
@@ -113,10 +135,28 @@ bool tbv_manager::set_and(tbv& dst,  tbv const& src) const {
     }
     return true;
 }
-tbv& tbv_manager::set_neg(tbv& dst) const {
-    m.set_neg(dst); 
-    return dst;
+
+void tbv_manager::complement(tbv const& src, ptr_vector<tbv>& result) {
+    tbv* r;
+    unsigned n = num_tbits();
+    for (unsigned i = 0; i < n; ++i) {
+        switch (src.get(i)) {
+        case BIT_0:
+            r = allocate(src);
+            r->set(i, BIT_1);
+            result.push_back(r);
+            break;
+        case BIT_1:
+            r = allocate(src);
+            r->set(i, BIT_0);
+            result.push_back(r);
+            break;
+        default:
+            break;
+        }
+    }
 }
+
 bool tbv_manager::equals(tbv const& a, tbv const& b) const {
     return m.equals(a, b);
 }
diff --git a/src/muz/ddnf/tbv.h b/src/muz/ddnf/tbv.h
index 626a942aa..190ad0cde 100644
--- a/src/muz/ddnf/tbv.h
+++ b/src/muz/ddnf/tbv.h
@@ -27,6 +27,7 @@ Revision History:
 class tbv;
 
 class tbv_manager {
+    friend class tbv;
     static const unsigned BIT_0 = 0x1;
     static const unsigned BIT_1 = 0x2;
     static const unsigned BIT_x = 0x3;
@@ -54,7 +55,7 @@ public:
     tbv& fillX(tbv& bv) const;
     bool set_and(tbv& dst,  tbv const& src) const;
     tbv& set_or(tbv& dst,  tbv const& src) const;
-    tbv& set_neg(tbv& dst) const;
+    void complement(tbv const& src, ptr_vector<tbv>& result);
     bool equals(tbv const& a, tbv const& b) const;
     unsigned hash(tbv const& src) const;
     bool contains(tbv const& a, tbv const& b) const;
@@ -65,8 +66,14 @@ public:
 class tbv: private fixed_bit_vector {
     friend class fixed_bit_vector_manager;
     friend class tbv_manager;
+
 public:
 
+    static const unsigned BIT_0 = tbv_manager::BIT_0;
+    static const unsigned BIT_1 = tbv_manager::BIT_1;
+    static const unsigned BIT_x = tbv_manager::BIT_x;
+    static const unsigned BIT_z = tbv_manager::BIT_z;
+
     struct eq {
         tbv_manager& m;
         eq(tbv_manager& m):m(m) {}
@@ -83,13 +90,19 @@ public:
         }
     };
         
-private:
+    void set(uint64 n, unsigned hi, unsigned lo);
+    void set(rational const& r, unsigned hi, unsigned lo);
+    void set(tbv const& other, unsigned hi, unsigned lo);
+
+    unsigned operator[](unsigned idx) { return get(idx); }
     void set(unsigned index, unsigned value) {
         SASSERT(value <= 3);
         fixed_bit_vector::set(2*index,   (value & 2) != 0);
         fixed_bit_vector::set(2*index+1, (value & 1) != 0);
     }
 
+private:
+
     unsigned get(unsigned index) const {
         index *= 2;
         return (fixed_bit_vector::get(index) << 1) | (unsigned)fixed_bit_vector::get(index+1);
diff --git a/src/muz/ddnf/udoc_relation.cpp b/src/muz/ddnf/udoc_relation.cpp
new file mode 100644
index 000000000..5e7e0f314
--- /dev/null
+++ b/src/muz/ddnf/udoc_relation.cpp
@@ -0,0 +1,274 @@
+#include "udoc_relation.h"
+#include "dl_relation_manager.h"
+
+namespace datalog {
+
+    udoc_relation::udoc_relation(udoc_plugin& p, relation_signature const& sig):
+        relation_base(p, sig),
+        dm(p.dm(num_signature_bits(p.bv, sig))) {
+        unsigned column = 0;
+        for (unsigned i = 0; i < sig.size(); ++i) {
+            m_column_info.push_back(column);
+            column += p.bv.get_bv_size(sig[i]);
+        }
+        m_column_info.push_back(column);
+    }
+    udoc_relation::~udoc_relation() {
+        reset();
+    }
+    unsigned udoc_relation::num_signature_bits(bv_util& bv, relation_signature const& sig) { 
+        unsigned result = 0;
+        for (unsigned i = 0; i < sig.size(); ++i) {
+            result += bv.get_bv_size(sig[i]);
+        }
+        return result;
+    }
+    void udoc_relation::reset() {
+        m_elems.reset(dm);
+    }
+    void udoc_relation::expand_column_vector(unsigned_vector& v, udoc_relation* other) const {
+        unsigned_vector orig;
+        orig.swap(v);
+        for (unsigned i = 0; i < orig.size(); ++i) {
+            unsigned col, limit;
+            if (orig[i] < get_num_cols()) {
+                col = column_idx(orig[i]);
+                limit = col + column_num_bits(orig[i]);
+            } else {
+                unsigned idx = orig[i] - get_num_cols();
+                col = get_num_bits() + other->column_idx(idx);
+                limit = col + other->column_num_bits(idx);
+            }
+            for (; col < limit; ++col) {
+                v.push_back(col);
+            }
+        }
+    }
+
+    doc* udoc_relation::fact2doc(const relation_fact & f) const {
+        doc* d = dm.allocate0();
+        for (unsigned i = 0; i < f.size(); ++i) {
+            unsigned bv_size;
+            rational val;
+            VERIFY(get_plugin().bv.is_numeral(f[i], val, bv_size));
+            SASSERT(bv_size == column_num_bits(i));
+            unsigned lo = column_idx(i);
+            unsigned hi = column_idx(i + 1);
+            d->pos().set(val, hi, lo);
+        }
+        return d;
+    }
+    void udoc_relation::add_fact(const relation_fact & f) {
+        doc* d = fact2doc(f);
+        m_elems.insert(dm, d);
+    }
+    bool udoc_relation::contains_fact(const relation_fact & f) const {
+        doc_ref d(dm, fact2doc(f));
+        return m_elems.contains(dm, *d);
+    }
+    udoc_relation * udoc_relation::clone() const {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    udoc_relation * udoc_relation::complement(func_decl* f) const {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    void udoc_relation::to_formula(expr_ref& fml) const {
+        NOT_IMPLEMENTED_YET();
+    }
+    udoc_plugin& udoc_relation::get_plugin() const {
+        return static_cast<udoc_plugin&>(relation_base::get_plugin());
+    }
+
+    void udoc_relation::display(std::ostream& out) const {
+        NOT_IMPLEMENTED_YET();
+    }
+
+    // -------------
+
+    udoc_plugin::udoc_plugin(relation_manager& rm):
+        relation_plugin(udoc_plugin::get_name(), rm),
+        m(rm.get_context().get_manager()),
+        bv(m) {
+    }
+    udoc_plugin::~udoc_plugin() {
+        u_map<doc_manager*>::iterator it = m_dms.begin(), end = m_dms.end();
+        for (; it != end; ++it) {
+            dealloc(it->m_value);
+        }
+    }
+    udoc_relation& udoc_plugin::get(relation_base& r) {
+        return dynamic_cast<udoc_relation&>(r);
+    }
+    udoc_relation* udoc_plugin::get(relation_base* r) {
+        return r?dynamic_cast<udoc_relation*>(r):0;
+    }
+    udoc_relation const & udoc_plugin::get(relation_base const& r) {
+        return dynamic_cast<udoc_relation const&>(r);        
+    }
+
+    doc_manager& udoc_plugin::dm(unsigned n) {
+        doc_manager* r;
+        if (!m_dms.find(n, r)) {
+            r = alloc(doc_manager, n);
+            m_dms.insert(n, r);
+        }
+        return *r;
+    }
+    bool udoc_plugin::can_handle_signature(const relation_signature & s) {
+        NOT_IMPLEMENTED_YET();
+        return false;
+    }
+    relation_base * udoc_plugin::mk_empty(const relation_signature & s) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_base * udoc_plugin::mk_full(func_decl* p, const relation_signature & s) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    class udoc_plugin::join_fn : public convenient_relation_join_fn {
+        doc_manager& dm;
+        doc_manager& dm1;
+        doc_manager& dm2;
+    public:
+        join_fn(udoc_plugin& p, udoc_relation const& t1, udoc_relation const& t2, unsigned col_cnt,
+                const unsigned * cols1, const unsigned * cols2) 
+            : convenient_relation_join_fn(t1.get_signature(), t2.get_signature(), col_cnt, cols1, cols2),
+              dm(p.dm(get_result_signature())),
+              dm1(t1.get_dm()),
+              dm2(t2.get_dm()) {
+            t1.expand_column_vector(m_cols1);
+            t2.expand_column_vector(m_cols2);
+        }
+
+        void join(doc const& d1, doc const& d2, udoc& result) {
+            doc* d = dm.allocateX();
+            tbv& pos = d->pos();
+            utbv& neg = d->neg();
+            unsigned mid = dm1.num_tbits();
+            unsigned hi  = dm.num_tbits();
+            pos.set(d1.pos(), mid-1, 0);
+            pos.set(d2.pos(), hi-1, mid);
+            // first fix bits
+            for (unsigned i = 0; i < m_cols1.size(); ++i) {
+                unsigned idx1 = m_cols1[i];
+                unsigned idx2 = mid + m_cols2[i];
+                unsigned v1 = pos[idx1];
+                unsigned v2 = pos[idx2];
+
+                if (v1 == tbv::BIT_x) {
+                    if (v2 != tbv::BIT_x)
+                        pos.set(idx1, v2);
+                } else if (v2 == tbv::BIT_x) {
+                    pos.set(idx2, v1);
+                } else if (v1 != v2) {
+                    dm.deallocate(d);
+                    // columns don't match
+                    return;
+                }
+            }
+            // fix equality of don't care columns
+            for (unsigned i = 0; i < m_cols1.size(); ++i) {
+                unsigned idx1 = m_cols1[i];
+                unsigned idx2 = mid + m_cols2[i];
+                unsigned v1 = pos[idx1];
+                unsigned v2 = pos[idx2];
+                
+                if (v1 == tbv::BIT_x && v2 == tbv::BIT_x) {
+                    // add to subtracted TBVs: 1xx0 and 0xx1
+                    tbv* r = dm.tbv().allocate(pos);
+                    r->set(idx1, tbv::BIT_0);
+                    r->set(idx2, tbv::BIT_1);
+                    neg.push_back(r);
+                    
+                    r = dm.tbv().allocate(pos);
+                    r->set(idx1, tbv::BIT_1);
+                    r->set(idx2, tbv::BIT_0);
+                    neg.push_back(r);
+                }
+            }
+
+            // handle subtracted TBVs:  1010 -> 1010xxx
+            for (unsigned i = 0; i < d1.neg().size(); ++i) {
+                tbv* t = dm.tbv().allocate();
+                t->set(d1.neg()[i], mid-1, 0);
+                t->set(d2.pos(), hi - 1, mid);
+                neg.push_back(t);
+            }
+            for (unsigned i = 0; i < d2.neg().size(); ++i) {
+                tbv* t = dm.tbv().allocate();
+                t->set(d1.pos(), mid-1, 0);
+                t->set(d2.neg()[i], hi - 1, mid);
+                neg.push_back(t);
+            }            
+            result.insert(dm, d);
+        }
+
+        virtual relation_base * operator()(const relation_base & _r1, const relation_base & _r2) {
+            udoc_relation const& r1 = get(_r1);
+            udoc_relation const& r2 = get(_r2);
+            udoc_plugin& p = r1.get_plugin();            
+            relation_signature const& sig = get_result_signature();
+            udoc_relation * result = alloc(udoc_relation, p, sig);
+            udoc const& d1 = r1.get_udoc();
+            udoc const& d2 = r2.get_udoc();
+            udoc& r = result->get_udoc();
+            for (unsigned i = 0; i < d1.size(); ++i) {
+                for (unsigned j = 0; j < d2.size(); ++j) {
+                    join(d1[i], d2[j], r);
+                }
+            }
+            return result;
+        }
+    };
+    relation_join_fn * udoc_plugin::mk_join_fn(
+        const relation_base & t1, const relation_base & t2,
+        unsigned col_cnt, const unsigned * cols1, const unsigned * cols2) {
+        if (!check_kind(t1) || !check_kind(t2)) {
+            return 0;
+        }
+        return alloc(join_fn, *this, get(t1), get(t2), col_cnt, cols1, cols2);
+    }
+    relation_transformer_fn * udoc_plugin::mk_project_fn(
+        const relation_base & t, unsigned col_cnt, 
+        const unsigned * removed_cols) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_transformer_fn * udoc_plugin::mk_rename_fn(
+        const relation_base & t, unsigned permutation_cycle_len, 
+        const unsigned * permutation_cycle) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_union_fn * udoc_plugin::mk_union_fn(
+        const relation_base & tgt, const relation_base & src, 
+        const relation_base * delta) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_union_fn * udoc_plugin::mk_widen_fn(
+        const relation_base & tgt, const relation_base & src, 
+        const relation_base * delta) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_mutator_fn * udoc_plugin::mk_filter_identical_fn(
+        const relation_base & t, unsigned col_cnt, 
+        const unsigned * identical_cols) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_mutator_fn * udoc_plugin::mk_filter_equal_fn(
+        const relation_base & t, const relation_element & value, unsigned col) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+    relation_mutator_fn * udoc_plugin::mk_filter_interpreted_fn(const relation_base & t, app * condition) {
+        NOT_IMPLEMENTED_YET();
+        return 0;
+    }
+
+}
diff --git a/src/muz/ddnf/udoc_relation.h b/src/muz/ddnf/udoc_relation.h
new file mode 100644
index 000000000..2dfa49553
--- /dev/null
+++ b/src/muz/ddnf/udoc_relation.h
@@ -0,0 +1,110 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    udoc_relation.h
+
+Abstract:
+
+    Relation based on union of DOCs.
+
+Author:
+
+    Nuno Lopes (a-nlopes) 2013-03-01
+    Nikolaj Bjorner (nbjorner) 2014-09-15
+
+Revision History:
+
+
+--*/
+
+#ifndef _UDOC_RELATION_H_
+#define _UDOC_RELATION_H_
+
+#include "doc.h"
+#include "dl_base.h"
+
+namespace datalog {
+    class udoc_plugin;
+    class udoc_relation;
+    
+    class udoc_relation : public relation_base {
+        friend class udoc_relation;
+        doc_manager&    dm;
+        udoc            m_elems;
+        unsigned_vector m_column_info;
+        static unsigned num_signature_bits(bv_util& bv, relation_signature const& sig);
+        doc* fact2doc(relation_fact const& f) const;        
+    public:
+        udoc_relation(udoc_plugin& p, relation_signature const& s);
+        virtual ~udoc_relation();
+        virtual void reset();
+        virtual void add_fact(const relation_fact & f);
+        virtual bool contains_fact(const relation_fact & f) const;
+        virtual udoc_relation * clone() const;
+        virtual udoc_relation * complement(func_decl*) const;
+        virtual void to_formula(expr_ref& fml) const;
+        udoc_plugin& get_plugin() const; 
+        virtual bool empty() const { return m_elems.empty(); }
+        virtual void display(std::ostream& out) const;
+        virtual bool is_precise() const { return true; }
+
+        doc_manager& get_dm() const { return dm; }
+        udoc const& get_udoc() const { return m_elems; }
+        udoc& get_udoc() { return m_elems; }
+        unsigned get_num_bits() const { return m_column_info.back(); }
+        unsigned get_num_cols() const { return m_column_info.size()-1; }
+        unsigned column_idx(unsigned col) const { return m_column_info[col]; }
+        unsigned column_num_bits(unsigned col) const { return m_column_info[col+1] - m_column_info[col]; }
+        void expand_column_vector(unsigned_vector& v, udoc_relation* other = 0) const;
+    };
+
+    class udoc_plugin : public relation_plugin {
+        friend class udoc_relation;
+        class join_fn;
+        class project_fn;
+        class union_fn;
+        class rename_fn;
+        class filter_mask_fn;
+        class filter_identical_fn;
+        class filter_interpreted_fn;
+        class filter_by_negation_fn;        
+        class filter_by_union_fn;
+        ast_manager& m;
+        bv_util      bv;
+        u_map<doc_manager*> m_dms;
+        doc_manager& dm(unsigned sz);
+        doc_manager& dm(relation_signature const& sig);
+        static udoc_relation& get(relation_base& r);
+        static udoc_relation* get(relation_base* r);
+        static udoc_relation const & get(relation_base const& r);   
+
+    public:
+        udoc_plugin(relation_manager& rm);
+        ~udoc_plugin();
+        virtual bool can_handle_signature(const relation_signature & s);
+        static symbol get_name() { return symbol("doc"); }
+        virtual relation_base * mk_empty(const relation_signature & s);
+        virtual relation_base * mk_full(func_decl* p, const relation_signature & s);
+        virtual relation_join_fn * mk_join_fn(const relation_base & t1, const relation_base & t2,
+            unsigned col_cnt, const unsigned * cols1, const unsigned * cols2);
+        virtual relation_transformer_fn * mk_project_fn(const relation_base & t, unsigned col_cnt, 
+            const unsigned * removed_cols);
+        virtual relation_transformer_fn * mk_rename_fn(const relation_base & t, unsigned permutation_cycle_len, 
+            const unsigned * permutation_cycle);
+        virtual relation_union_fn * mk_union_fn(const relation_base & tgt, const relation_base & src, 
+            const relation_base * delta);
+        virtual relation_union_fn * mk_widen_fn(const relation_base & tgt, const relation_base & src, 
+            const relation_base * delta);
+        virtual relation_mutator_fn * mk_filter_identical_fn(const relation_base & t, unsigned col_cnt, 
+            const unsigned * identical_cols);
+        virtual relation_mutator_fn * mk_filter_equal_fn(const relation_base & t, const relation_element & value, 
+            unsigned col);
+        virtual relation_mutator_fn * mk_filter_interpreted_fn(const relation_base & t, app * condition);
+        // project join select
+    };
+};
+       
+#endif /* _UDOC_RELATION_H_ */
+