diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 439d60bbf..2b6027a02 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -126,14 +126,16 @@ eautomaton* re2automaton::re2aut(expr* e) {
         }
         return b.detach();        
     }
-#if 0
     else if (u.re.is_empty(e)) {
-        return alloc(eautomaton, m);
+        return alloc(eautomaton, sm);
     }
     else if (u.re.is_full(e)) {
+        sym_expr* _true = sym_expr::mk_pred(expr_ref(m.mk_true(), m));
+        return eautomaton::mk_loop(sm, _true);
     }
+#if 0
     else if (u.re.is_intersect(e, e1, e2)) {
-
+        // maybe later
     }
 #endif
     
@@ -1127,7 +1129,6 @@ bool seq_rewriter::reduce_eq(expr_ref_vector& ls, expr_ref_vector& rs, expr_ref_
         if (set_empty(szr, _rs, true, lhs, rhs)) {
             lchange |= szr > 1; 
             change  |= szr > 1;
-            TRACE("seq", tout << lchange << " " << szr << "\n";);
             if (szr == 1 && !lchange) {
                 lhs.reset();
                 rhs.reset();
@@ -1322,23 +1323,20 @@ bool seq_rewriter::is_subsequence(unsigned szl, expr* const* l, unsigned szr, ex
     for (unsigned i = 0; i < szl; ++i) {
         bool found = false;
         unsigned j = 0;
+        bool is_unit = m_util.str.is_unit(l[i]);
         for (; !found && j < szr; ++j) {
-            found = !rpos.contains(j) && l[i] == r[j];
+            found = !rpos.contains(j) && (l[i] == r[j] || (is_unit && m_util.str.is_unit(r[j])));
         }
+        
         if (!found) {
-#if 0
-            std::cout << mk_pp(l[i], m()) << " not found in ";
-            for (unsigned j = 0; j < szr; ++j) {
-                std::cout << mk_pp(r[j], m()) << " ";
-            }
-            std::cout << "\n";
-#endif
             return false;
         }
         SASSERT(0 < j && j <= szr);
         rpos.insert(j-1);
     }
     // if we reach here, then every element of l is contained in r in some position.
+    // or each non-unit in l is matched by a non-unit in r, and otherwise, the non-units match up.
+    bool change = false;
     ptr_vector<expr> rs;
     for (unsigned j = 0; j < szr; ++j) {
         if (rpos.contains(j)) {
@@ -1348,6 +1346,12 @@ bool seq_rewriter::is_subsequence(unsigned szl, expr* const* l, unsigned szr, ex
             is_sat = false;
             return true;
         }
+        else {
+            change = true;
+        }
+    }
+    if (!change) {
+        return false;
     }
     SASSERT(szl == rs.size());
     if (szl > 0) {
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index 66ff7116a..393556b58 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -36,18 +36,55 @@ static bool is_hex_digit(char ch, unsigned& d) {
 
 static bool is_escape_char(char const *& s, unsigned& result) {
     unsigned d1, d2;
-    if (*s == '\\' && *(s + 1) == 'x' && 
+    if (*s != '\\' || *(s + 1) == 0) {
+        return false;
+    }
+    if (*(s + 1) == 'x' && 
         is_hex_digit(*(s + 2), d1) && is_hex_digit(*(s + 3), d2)) {
         result = d1*16 + d2;
         s += 4;
         return true;
     }
-    if (*s == '\\' && *(s + 1) == '\\') {
-        result = '\\';
+    switch (*(s + 1)) {
+    case 'a':
+        result = '\a';
+        s += 2;
+        return true;
+    case 'b':
+        result = '\b';
+        s += 2;
+        return true;
+#if 0
+    case 'e':
+        result = '\e';
+        s += 2;
+        return true;
+#endif
+    case 'f':
+        result = '\f';
+        s += 2;
+        return true;
+    case 'n':
+        result = '\n';
+        s += 2;
+        return true;
+    case 'r':
+        result = '\r';
+        s += 2;
+        return true;
+    case 't':
+        result = '\t';
+        s += 2;
+        return true;
+    case 'v':
+        result = '\v';
+        s += 2;
+        return true;
+    default:
+        result = *(s + 1);
         s += 2;
         return true;
     }
-    return false;
 }
 
 zstring::zstring(encoding enc): m_encoding(enc) {}
@@ -411,9 +448,9 @@ void seq_decl_plugin::init() {
     m_sigs[OP_RE_UNION]      = alloc(psig, m, "re.union",     1, 2, reAreA, reA);
     m_sigs[OP_RE_INTERSECT]  = alloc(psig, m, "re.inter",     1, 2, reAreA, reA);
     m_sigs[OP_RE_LOOP]           = alloc(psig, m, "re.loop",    1, 1, &reA, reA);
-    m_sigs[OP_RE_EMPTY_SET]      = alloc(psig, m, "re-empty-set", 1, 0, 0, reA);
-    m_sigs[OP_RE_FULL_SET]       = alloc(psig, m, "re-full-set", 1, 0, 0, reA);
-    m_sigs[OP_RE_OF_PRED]        = alloc(psig, m, "re-of-pred", 1, 1, &predA, reA);
+    m_sigs[OP_RE_EMPTY_SET]      = alloc(psig, m, "re.empty", 1, 0, 0, reA);
+    m_sigs[OP_RE_FULL_SET]       = alloc(psig, m, "re.all", 1, 0, 0, reA);
+    m_sigs[OP_RE_OF_PRED]        = alloc(psig, m, "re.of.pred", 1, 1, &predA, reA);
     m_sigs[OP_SEQ_TO_RE]         = alloc(psig, m, "seq.to.re",  1, 1, &seqA, reA);
     m_sigs[OP_SEQ_IN_RE]         = alloc(psig, m, "seq.in.re", 1, 2, seqAreA, boolT);
     m_sigs[OP_STRING_CONST]      = 0;
@@ -429,6 +466,8 @@ void seq_decl_plugin::init() {
     m_sigs[_OP_STRING_SUFFIX]    = alloc(psig, m, "str.suffixof", 0, 2, str2T, boolT);
     m_sigs[_OP_STRING_IN_REGEXP]  = alloc(psig, m, "str.in.re", 0, 2, strTreT, boolT);
     m_sigs[_OP_STRING_TO_REGEXP]  = alloc(psig, m, "str.to.re", 0, 1, &strT, reT);
+    m_sigs[_OP_REGEXP_EMPTY]      = alloc(psig, m, "re.nostr", 0, 0, 0, reT);
+    m_sigs[_OP_REGEXP_FULL]       = alloc(psig, m, "re.allchar", 0, 0, 0, reT);
     m_sigs[_OP_STRING_SUBSTR]     = alloc(psig, m, "str.substr", 0, 3, strTint2T, strT);
 }
 
@@ -527,6 +566,13 @@ func_decl * seq_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters,
         match(*m_sigs[k], arity, domain, range, rng);
         return m.mk_func_decl(m_sigs[k]->m_name, arity, domain, rng, func_decl_info(m_family_id, k));
 
+    case _OP_REGEXP_FULL:
+        match(*m_sigs[k], arity, domain, range, rng);
+        return m.mk_func_decl(symbol("re.allchar"), arity, domain, rng, func_decl_info(m_family_id, OP_RE_FULL_SET));
+    case _OP_REGEXP_EMPTY:
+        match(*m_sigs[k], arity, domain, range, rng);
+        return m.mk_func_decl(symbol("re.nostr"), arity, domain, rng, func_decl_info(m_family_id, OP_RE_EMPTY_SET));
+        
     case OP_RE_LOOP:
         match(*m_sigs[k], arity, domain, range, rng);
         if (num_parameters != 2 || !parameters[0].is_int() || !parameters[1].is_int()) {
diff --git a/src/ast/seq_decl_plugin.h b/src/ast/seq_decl_plugin.h
index e97e92962..ecb118581 100644
--- a/src/ast/seq_decl_plugin.h
+++ b/src/ast/seq_decl_plugin.h
@@ -74,7 +74,9 @@ enum seq_op_kind {
     _OP_STRING_TO_REGEXP, 
     _OP_STRING_CHARAT, 
     _OP_STRING_SUBSTR,      
-    _OP_STRING_STRIDOF, 
+    _OP_STRING_STRIDOF,
+    _OP_REGEXP_EMPTY,
+    _OP_REGEXP_FULL,
     _OP_SEQ_SKOLEM,
     LAST_SEQ_OP
 };
diff --git a/src/ast/simplifier/simplifier.cpp b/src/ast/simplifier/simplifier.cpp
index 5358e01e4..2a152283f 100644
--- a/src/ast/simplifier/simplifier.cpp
+++ b/src/ast/simplifier/simplifier.cpp
@@ -127,11 +127,11 @@ bool simplifier::get_subst(expr * n, expr_ref & r, proof_ref & p) {
     return false;
 }
 
-void simplifier::reduce_core(expr * n) {
-    if (!is_cached(n)) {
+void simplifier::reduce_core(expr * n1) {
+    if (!is_cached(n1)) {
         // We do not assume m_todo is empty... So, we store the current size of the todo-stack.
         unsigned sz = m_todo.size();
-        m_todo.push_back(n);
+        m_todo.push_back(n1);
         while (m_todo.size() != sz) {
             expr * n = m_todo.back();
             if (is_cached(n))
@@ -142,6 +142,10 @@ void simplifier::reduce_core(expr * n) {
                 m_todo.pop_back();
                 reduce1(n);
             }
+            if (m.canceled()) {
+                cache_result(n1, n1, 0);
+                break;
+            }
         }
     }
 }
diff --git a/src/smt/theory_seq.cpp b/src/smt/theory_seq.cpp
index c7fab3934..185e92ea2 100644
--- a/src/smt/theory_seq.cpp
+++ b/src/smt/theory_seq.cpp
@@ -444,7 +444,9 @@ bool theory_seq::check_length_coherence(expr* e) {
             propagate_is_conc(e, conc);
             assume_equality(tail, emp);
         }
-        m_trail_stack.push(push_replay(alloc(replay_length_coherence, m, e)));
+        if (!get_context().at_base_level()) {
+            m_trail_stack.push(push_replay(alloc(replay_length_coherence, m, e)));
+        }
         return true;
     }
     return false;
@@ -652,7 +654,7 @@ bool theory_seq::simplify_eq(expr_ref_vector& ls, expr_ref_vector& rs, dependenc
     expr_ref_vector lhs(m), rhs(m);
     bool changed = false;
     if (!m_seq_rewrite.reduce_eq(ls, rs, lhs, rhs, changed)) {
-        // equality is inconsistent.x2
+        // equality is inconsistent.
         TRACE("seq", tout << ls << " != " << rs << "\n";);
         set_conflict(deps);
         return true;
@@ -1534,7 +1536,7 @@ void theory_seq::propagate() {
     }
     while (!m_replay.empty() && !ctx.inconsistent()) {
         (*m_replay[m_replay.size()-1])(*this);
-        TRACE("seq", tout << "replay: " << ctx.get_scope_level() << "\n";);
+        TRACE("seq", tout << "replay at level: " << ctx.get_scope_level() << "\n";);
         m_replay.pop_back();
     }
     if (m_new_solution) {
@@ -1716,6 +1718,7 @@ void theory_seq::add_elim_string_axiom(expr* n) {
     - len(x) >= 0                   otherwise
  */
 void theory_seq::add_length_axiom(expr* n) {
+    context& ctx = get_context();
     expr* x;
     VERIFY(m_util.str.is_length(n, x));
     if (m_util.str.is_concat(x) ||
@@ -1726,12 +1729,15 @@ void theory_seq::add_length_axiom(expr* n) {
         m_rewrite(len);
         SASSERT(n != len);
         add_axiom(mk_eq(len, n, false));
-
-        m_trail_stack.push(push_replay(alloc(replay_axiom, m, n)));
+        if (!ctx.at_base_level()) {
+            m_trail_stack.push(push_replay(alloc(replay_axiom, m, n)));
+        }
     }
     else {
         add_axiom(mk_literal(m_autil.mk_ge(n, m_autil.mk_int(0))));        
-        m_trail_stack.push(push_replay(alloc(replay_axiom, m, n)));
+        if (!ctx.at_base_level()) {
+            m_trail_stack.push(push_replay(alloc(replay_axiom, m, n)));
+        }
     }
 }