diff --git a/.gitignore b/.gitignore
index df4e3266d..8e5bd7294 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ crashes/
 *.pyo
 # Ignore callgrind files
 callgrind.out.*
+gmon.out
 # .hpp files are automatically generated
 *.hpp
 .env
diff --git a/gmon.out b/gmon.out
deleted file mode 100644
index cba10a19b..000000000
Binary files a/gmon.out and /dev/null differ
diff --git a/src/ast/rewriter/CMakeLists.txt b/src/ast/rewriter/CMakeLists.txt
index 10f7130ec..3c5f6defe 100644
--- a/src/ast/rewriter/CMakeLists.txt
+++ b/src/ast/rewriter/CMakeLists.txt
@@ -39,6 +39,7 @@ z3_add_component(rewriter
     rewriter.cpp
     seq_axioms.cpp
     seq_eq_solver.cpp
+    seq_derive.cpp
     seq_subset.cpp
     seq_derive.cpp
     seq_rewriter.cpp
diff --git a/src/ast/rewriter/seq_derive.cpp b/src/ast/rewriter/seq_derive.cpp
index 4f0233961..8f5831086 100644
--- a/src/ast/rewriter/seq_derive.cpp
+++ b/src/ast/rewriter/seq_derive.cpp
@@ -615,9 +615,16 @@ namespace seq {
     }
 
     bool derive::pred_implies(expr* a, expr* b) {
+<<<<<<< HEAD
         bool sign_a = m.is_not(a, a);
         bool sign_b = m.is_not(b, b);
         return pred_implies(sign_a, a, sign_b, b);
+=======
+        expr* nota = nullptr, * notb = nullptr;
+        bool sign_a = m.is_not(a, nota);
+        bool sign_b = m.is_not(b, notb);
+        return pred_implies(sign_a, sign_a ? nota : a, sign_b, sign_b ? notb : b);
+>>>>>>> b5afa9200e22209daec4b6d64831f89b8b1dc822
     }
 
     expr_ref derive::mk_union(expr* a, expr* b) {
@@ -748,11 +755,14 @@ namespace seq {
             return expr_ref(re().mk_to_re(u().str.mk_concat(s1, s2)), m);
 
         // r* · r* → r*
+
         expr* a1 = nullptr, *a2 = nullptr, * b1 = nullptr;
+
         if (re().is_star(a, a1) && re().is_star(b, b1) && a1 == b1)
             return expr_ref(a, m);
 
         // Right-associate: (a · b) · c → a · (b · c)
+
         if (re().is_concat(a, a1, a2)) 
             return mk_concat(a1, mk_concat(a2, b));
         
@@ -883,6 +893,7 @@ namespace seq {
         expr* saved_path_expr = m_path_expr;
 
         // Push atoms onto path and check for contradiction or implication
+<<<<<<< HEAD
         lbool result = push_path_atoms(c, sign);
         if (result != l_undef) {
             m_path.shrink(saved_path_sz);
@@ -898,6 +909,31 @@ namespace seq {
             m_intervals.shrink(saved_intervals_sz);
             m_intervals_start = saved_intervals_start;
             return result;
+=======
+        lbool atoms_result = push_path_atoms(c, sign);
+        if (atoms_result == l_false) {
+            m_path.shrink(saved_path_sz);
+            m_intervals.shrink(saved_intervals_sz);
+            m_intervals_start = saved_intervals_start;
+            return l_false;
+        }
+
+        // Update intervals
+        lbool intervals_result = push_intervals_impl(c, sign);
+        if (intervals_result == l_false) {
+            m_path.shrink(saved_path_sz);
+            m_intervals.shrink(saved_intervals_sz);
+            m_intervals_start = saved_intervals_start;
+            return l_false;
+        }
+
+        // If either determined the atom is implied, no need to actually push
+        if (atoms_result == l_true || intervals_result == l_true) {
+            m_path.shrink(saved_path_sz);
+            m_intervals.shrink(saved_intervals_sz);
+            m_intervals_start = saved_intervals_start;
+            return l_true;
+>>>>>>> b5afa9200e22209daec4b6d64831f89b8b1dc822
         }
 
         // Update path expression
diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index a4d7816b5..73a5e6417 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -2613,8 +2613,7 @@ expr_ref seq_rewriter::is_nullable(expr* r) {
     return result;
 }
 
-
-/ ()
+/*
     Push reverse inwards (whenever possible).
 */
 br_status seq_rewriter::mk_re_reverse(expr* r, expr_ref& result) {
@@ -2842,14 +2841,6 @@ expr_ref seq_rewriter::mk_derivative(expr* r) {
     return result;
 }
 
-expr_ref seq_rewriter::mk_brz_derivative(expr* r) {
-    sort* seq_sort = nullptr, * ele_sort = nullptr;
-    VERIFY(m_util.is_re(r, seq_sort));
-    VERIFY(m_util.is_seq(seq_sort, ele_sort));
-    expr_ref v(m().mk_var(0, ele_sort), m());
-    return mk_derivative_rec(v, r);
-}
-
 expr_ref seq_rewriter::mk_derivative(expr* ele, expr* r) {
     auto result = m_derive(ele, r);
     TRACE(seq,
@@ -3010,6 +3001,7 @@ expr_ref seq_rewriter::merge_regex_sets(expr* r1, expr* r2, expr* unit,
         return composeresult(ar);
     }
 }
+
 /*
 * calls elim_condition
 */
@@ -3396,7 +3388,6 @@ expr_ref seq_rewriter::mk_der_cond(expr* cond, expr* ele, sort* seq_sort) {
 }
 
 
-
 /*************************************************
  *****          End Derivative Code          *****
  *************************************************/
diff --git a/src/ast/rewriter/seq_rewriter.h b/src/ast/rewriter/seq_rewriter.h
index 62f79bd99..7b8058353 100644
--- a/src/ast/rewriter/seq_rewriter.h
+++ b/src/ast/rewriter/seq_rewriter.h
@@ -139,8 +139,14 @@ class seq_rewriter {
     // re2automaton   m_re2aut;
     op_cache       m_op_cache;
     expr_ref_vector m_es, m_lhs, m_rhs;
+<<<<<<< HEAD
     bool           m_coalesce_chars;
     bool           m_in_bisim { false };
+=======
+    bool           m_coalesce_chars;    
+    unsigned       m_re_deriv_depth { 0 };
+    static const unsigned m_max_re_deriv_depth = 512;
+>>>>>>> b5afa9200e22209daec4b6d64831f89b8b1dc822
 
     enum length_comparison {
         shorter_c, 
@@ -332,7 +338,7 @@ class seq_rewriter {
 
 public:
     seq_rewriter(ast_manager & m, params_ref const & p = params_ref()):
-        m_util(m), m_subset(m_util.re), m_autil(m), m_br(m, p), m_derive(m, *this),  // m_re2aut(m), 
+        m_util(m), m_subset(m_util.re), m_autil(m), m_br(m, p), m_derive(m, *this),
         m_op_cache(m), m_es(m), 
         m_lhs(m), m_rhs(m) {
     }
diff --git a/src/ast/rewriter/seq_subset.cpp b/src/ast/rewriter/seq_subset.cpp
index 2fc4d1f71..f12bc32b1 100644
--- a/src/ast/rewriter/seq_subset.cpp
+++ b/src/ast/rewriter/seq_subset.cpp
@@ -19,7 +19,7 @@ Author:
 
 bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
     while (true) {
-        
+
         if (a == b)
             return true;
         if (m_re.is_empty(a))
@@ -30,7 +30,7 @@ bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
             return true;
 
         if (depth >= m_max_depth)
-            return false;        
+            return false;
 
         expr* a1 = nullptr, * a2 = nullptr, * b1 = nullptr, * b2 = nullptr;
         unsigned la, ua, lb, ub;
@@ -39,16 +39,12 @@ bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
         if (m_re.is_dot_plus(b) && m_re.get_info(a).nullable == l_false)
             return true;
 
-        // a ⊆ a*
-        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth))
-            return true;
-
         // e ⊆ a*
         if (m_re.is_epsilon(a) && m_re.is_star(b, b1))
             return true;
 
-        // R ⊆ R*
-        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth + 1))
+        // a ⊆ a*: if b = b1* and a ⊆ b1, then a ⊆ b1*
+        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth))
             return true;
 
         // R1* ⊆ R2* if R1 ⊆ R2