diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 1cbc2d288..879aa2144 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -222,7 +222,8 @@ br_status seq_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * con
     case OP_RE_RANGE:
         return BR_FAILED;    
     case OP_RE_INTERSECT:
-        return BR_FAILED;    
+        SASSERT(num_args == 2);
+        return mk_re_inter(args[0], args[1], result);
     case OP_RE_LOOP:
         return mk_re_loop(num_args, args, result);
     case OP_RE_EMPTY_SET:
@@ -788,6 +789,14 @@ bool seq_rewriter::is_sequence(expr* e, expr_ref_vector& seq) {
 }
 
 br_status seq_rewriter::mk_str_in_regexp(expr* a, expr* b, expr_ref& result) {
+    if (m_util.re.is_empty(b)) {
+        result = m().mk_false();
+        return BR_DONE;
+    }
+    if (m_util.re.is_full(b)) {
+        result = m().mk_true();
+        return BR_DONE;
+    }
     scoped_ptr<eautomaton> aut;
     expr_ref_vector seq(m());
     if (!(aut = m_re2aut(b))) {
@@ -935,6 +944,38 @@ br_status seq_rewriter::mk_re_union(expr* a, expr* b, expr_ref& result) {
 }
 
 
+/**
+   (emp n r) = emp
+   (r n emp) = emp
+   (all n r) = r
+   (r n all) = r
+   (r n r) = r
+ */
+br_status seq_rewriter::mk_re_inter(expr* a, expr* b, expr_ref& result) {
+    if (a == b) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_empty(a)) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_empty(b)) {
+        result = b;
+        return BR_DONE;
+    }
+    if (m_util.re.is_full(a)) {
+        result = b;
+        return BR_DONE;
+    }
+    if (m_util.re.is_full(b)) {
+        result = a;
+        return BR_DONE;
+    }
+    return BR_FAILED;
+}
+
+
 br_status seq_rewriter::mk_re_loop(unsigned num_args, expr* const* args, expr_ref& result) {
     rational n1, n2;
     switch (num_args) {
@@ -964,13 +1005,26 @@ br_status seq_rewriter::mk_re_loop(unsigned num_args, expr* const* args, expr_re
   (a* + b)* = (a + b)*
   (a + b*)* = (a + b)*
   (a*b*)*   = (a + b)*
+   a+* = a*
+   emp* = ""
+   all* = all   
 */
 br_status seq_rewriter::mk_re_star(expr* a, expr_ref& result) {
     expr* b, *c, *b1, *c1;
-    if (m_util.re.is_star(a) || m_util.re.is_empty(a) || m_util.re.is_full(a)) {
+    if (m_util.re.is_star(a) || m_util.re.is_full(a)) {
         result = a;
         return BR_DONE;
     }
+    if (m_util.re.is_empty(a)) {
+        sort* seq_sort = 0;
+        VERIFY(m_util.is_re(a, seq_sort));
+        result = m_util.re.mk_to_re(m_util.str.mk_empty(seq_sort));
+        return BR_DONE;
+    }
+    if (m_util.re.is_plus(a, b)) {
+        result = m_util.re.mk_star(b);
+        return BR_DONE;
+    }
     if (m_util.re.is_union(a, b, c)) {
         if (m_util.re.is_star(b, b1)) {
             result = m_util.re.mk_star(m_util.re.mk_union(b1, c));
@@ -980,6 +1034,14 @@ br_status seq_rewriter::mk_re_star(expr* a, expr_ref& result) {
             result = m_util.re.mk_star(m_util.re.mk_union(b, c1));
             return BR_REWRITE2;
         }
+        if (is_epsilon(b)) {
+            result = m_util.re.mk_star(c);
+            return BR_REWRITE2;
+        }
+        if (is_epsilon(c)) {
+            result = m_util.re.mk_star(b);
+            return BR_REWRITE2;
+        }
     }
     if (m_util.re.is_concat(a, b, c) &&
         m_util.re.is_star(b, b1) && m_util.re.is_star(c, c1)) {
@@ -991,9 +1053,34 @@ br_status seq_rewriter::mk_re_star(expr* a, expr_ref& result) {
 }
 
 /*
+   emp+ = emp
+   all+ = all
+   a*+ = a*
+   a++ = a+
    a+ = aa*
 */
 br_status seq_rewriter::mk_re_plus(expr* a, expr_ref& result) {
+    if (m_util.re.is_empty(a)) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_full(a)) {
+        result = a;
+        return BR_DONE;
+    }
+    if (is_epsilon(a)) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_plus(a)) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_star(a)) {
+        result = a;
+        return BR_DONE;
+    }
+
     return BR_FAILED;
 //  result = m_util.re.mk_concat(a, m_util.re.mk_star(a));
 //  return BR_REWRITE2;
diff --git a/src/ast/rewriter/seq_rewriter.h b/src/ast/rewriter/seq_rewriter.h
index 89cbb2566..ee1ba42e2 100644
--- a/src/ast/rewriter/seq_rewriter.h
+++ b/src/ast/rewriter/seq_rewriter.h
@@ -95,6 +95,7 @@ class seq_rewriter {
     br_status mk_str_to_regexp(expr* a, expr_ref& result);
     br_status mk_re_concat(expr* a, expr* b, expr_ref& result);
     br_status mk_re_union(expr* a, expr* b, expr_ref& result);
+    br_status mk_re_inter(expr* a, expr* b, expr_ref& result);
     br_status mk_re_star(expr* a, expr_ref& result);
     br_status mk_re_plus(expr* a, expr_ref& result);
     br_status mk_re_opt(expr* a, expr_ref& result);
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index 5bbc26e6d..c137801ff 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -612,9 +612,8 @@ func_decl * seq_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters,
                                func_decl_info(m_family_id, OP_STRING_CONST, num_parameters, parameters));
         
     case OP_RE_UNION:
-        return mk_assoc_fun(k, arity, domain, range, k, k);
-
     case OP_RE_CONCAT:  
+    case OP_RE_INTERSECT:  
         return mk_assoc_fun(k, arity, domain, range, k, k);
 
     case OP_SEQ_CONCAT: 
diff --git a/src/math/automata/automaton.h b/src/math/automata/automaton.h
index a5acc18af..54c969bbb 100644
--- a/src/math/automata/automaton.h
+++ b/src/math/automata/automaton.h
@@ -105,6 +105,8 @@ public:
     // create an automaton from initial state, final states, and moves
     automaton(M& m, unsigned init, unsigned_vector const& final, moves const& mvs): m(m) {
         m_init = init;
+        m_delta.push_back(moves());
+        m_delta_inv.push_back(moves());
         for (unsigned i = 0; i < final.size(); ++i) {
             add_to_final_states(final[i]);
         }
@@ -331,6 +333,7 @@ public:
     //  Src - ET -> dst - e -> dst1 => Src - ET -> dst1  if out_degree(dst) = 1, 
     //
     void compress() {
+        SASSERT(!m_delta.empty());
         for (unsigned i = 0; i < m_delta.size(); ++i) {
             for (unsigned j = 0; j < m_delta[i].size(); ++j) {
                 move const& mv = m_delta[i][j];
@@ -419,6 +422,7 @@ public:
                 }
             }
         }
+        SASSERT(!m_delta.empty());
         while (true) {
             SASSERT(!m_delta.empty());
             unsigned src = m_delta.size() - 1;