diff --git a/src/sat/sat_aig_cuts.cpp b/src/sat/sat_aig_cuts.cpp
index c1bf18ac7..8d93a1604 100644
--- a/src/sat/sat_aig_cuts.cpp
+++ b/src/sat/sat_aig_cuts.cpp
@@ -132,7 +132,7 @@ namespace sat {
         SASSERT(n.is_and() && n.size() == 0);
         reset(cs);
         cut c;          
-        c.m_table = (n.sign() ? 0x0 : 0x1);
+        c.set_table(n.sign() ? 0x0 : 0x1);
         push_back(cs, c);
     }
 
@@ -212,11 +212,6 @@ namespace sat {
         }        
     }
 
-    void aig_cuts::replace(unsigned v, cut const& src, cut const& dst) {
-        m_cuts[v].replace(m_on_cut_add, m_on_cut_del, src, dst);
-        touch(v);
-    }
-
 
     bool aig_cuts::is_touched(node const& n) {
         for (unsigned i = 0; i < n.size(); ++i) {
@@ -459,7 +454,7 @@ namespace sat {
                 m_clause.push_back(lit);                
             }
             literal rr = r;
-            if (0 == (c.m_table & (1ull << i))) rr.neg();
+            if (0 == (c.table() & (1ull << i))) rr.neg();
             m_clause.push_back(rr);
             on_clause(m_clause);
         }
diff --git a/src/sat/sat_aig_cuts.h b/src/sat/sat_aig_cuts.h
index feefb7ec8..879241737 100644
--- a/src/sat/sat_aig_cuts.h
+++ b/src/sat/sat_aig_cuts.h
@@ -109,7 +109,6 @@ namespace sat {
         bool is_touched(node const& n);
         bool is_touched(literal lit) const { return is_touched(lit.var()); }
         bool is_touched(bool_var v) const { return m_last_touched[v] + m_aig.size() >= m_num_cut_calls * m_aig.size(); }
-        void touch(bool_var v) { m_last_touched[v] = v + m_num_cut_calls * m_aig.size(); }
         void reserve(unsigned v);
         bool insert_aux(unsigned v, node const& n);
         void init_cut_set(unsigned id);
@@ -166,7 +165,7 @@ namespace sat {
 
         void cut2def(on_clause_t& on_clause, cut const& c, literal r);
 
-        void replace(unsigned v, cut const& src, cut const& dst);
+        void touch(bool_var v) { m_last_touched[v] = v + m_num_cut_calls * m_aig.size(); }
 
 
         std::ostream& display(std::ostream& out) const;
diff --git a/src/sat/sat_aig_simplifier.cpp b/src/sat/sat_aig_simplifier.cpp
index a94e131dd..3f2017701 100644
--- a/src/sat/sat_aig_simplifier.cpp
+++ b/src/sat/sat_aig_simplifier.cpp
@@ -463,19 +463,14 @@ namespace sat {
             rep(cut const& s, cut const& d, unsigned v):src(s), dst(d), v(v) {} 
             rep():v(UINT_MAX) {}
         };
-        vector<rep> to_replace;
-        cut d;
-        for (auto const& cs : cuts) {
+        for (auto& cs : cuts) {
             for (auto const& c : cs) {
-                if (rewrite_cut(c, d)) {
-                    to_replace.push_back(rep(c, d, cs.var()));
+                if (add_dont_care(c)) {
+                    m_aig_cuts.touch(cs.var());
+                    m_stats.m_num_dont_care_reductions++;
                 }
             }
         }
-        for (auto const& p : to_replace) {
-            m_aig_cuts.replace(p.v, p.src, p.dst);
-        }
-        m_stats.m_num_dont_care_reductions += to_replace.size();
     }
 
     /*
@@ -497,18 +492,18 @@ namespace sat {
     /**
      * apply obtained dont_cares to cut sets.
      */
-    bool aig_simplifier::rewrite_cut(cut const& c, cut& d) {
-        bool init = false;
+    bool aig_simplifier::add_dont_care(cut const & c) {
+        uint64_t dc = 0;
         for (unsigned i = 0; i < c.size(); ++i) {
             for (unsigned j = i + 1; j < c.size(); ++j) {
                 var_pair p(c[i], c[j]);
                 if (m_pairs.find(p, p) && p.op != none) {
-                    if (!init) { d = c; init = true; }
-                    d.set_table(d.m_table | op2dont_care(i, j, p));
+                    dc |= op2dont_care(i, j, p);
                 }
             }
         }
-        return init && d.m_table != c.m_table;
+        
+        return (dc != c.dont_care()) && (c.add_dont_care(dc), true);
     }
 
     void aig_simplifier::collect_statistics(statistics& st) const {
diff --git a/src/sat/sat_aig_simplifier.h b/src/sat/sat_aig_simplifier.h
index ba5d40561..73b27aa67 100644
--- a/src/sat/sat_aig_simplifier.h
+++ b/src/sat/sat_aig_simplifier.h
@@ -95,7 +95,7 @@ namespace sat {
         void cuts2pairs(vector<cut_set> const& cuts);
         void pairs2dont_cares();
         void dont_cares2cuts(vector<cut_set> const& cuts);
-        bool rewrite_cut(cut const& c, cut& r);
+        bool add_dont_care(cut const & c);
         uint64_t op2dont_care(unsigned i, unsigned j, var_pair const& p);
 
     public:
diff --git a/src/sat/sat_cutset.cpp b/src/sat/sat_cutset.cpp
index 3b56b02ab..e43c74852 100644
--- a/src/sat/sat_cutset.cpp
+++ b/src/sat/sat_cutset.cpp
@@ -88,17 +88,6 @@ namespace sat {
         m_cuts[m_size++] = c; 
     }
 
-    void cut_set::replace(on_update_t& on_add, on_update_t& on_del, cut const& src, cut const& dst) {
-        SASSERT(src != dst);
-        insert(on_add, on_del, dst);
-        for (unsigned i = 0; i < size(); ++i) {
-            if (src == (*this)[i]) {
-                evict(on_del, i);
-                break;
-            }
-        }
-    }
-
     void cut_set::evict(on_update_t& on_del, unsigned idx) {
         if (m_var != UINT_MAX && on_del) on_del(m_var, m_cuts[idx]); 
         m_cuts[idx] = m_cuts[--m_size]; 
@@ -146,12 +135,12 @@ namespace sat {
             y = c[++j];
         }
         index |= (1 << c.m_size);
-        return compute_shift(m_table, index);
+        return compute_shift(table(), index);
     }
     
     bool cut::operator==(cut const& other) const {
         if (m_size != other.m_size) return false;
-        if (m_table != other.m_table) return false;
+        if (table() != other.table()) return false;
         for (unsigned i = 0; i < m_size; ++i) {
             if ((*this)[i] != other[i]) return false;
         }
@@ -160,7 +149,7 @@ namespace sat {
     
     unsigned cut::hash() const {
         return get_composite_hash(*this, m_size, 
-                                  [](cut const& c) { return (unsigned)c.m_table; }, 
+                                  [](cut const& c) { return (unsigned)c.table(); }, 
                                   [](cut const& c, unsigned i) { return c[i]; });
     }
     
@@ -172,7 +161,7 @@ namespace sat {
         }        
         out << "} ";
         for (unsigned i = 0; i < (1u << m_size); ++i) {
-            if (0 != (m_table & (1ull << i))) out << "1"; else out << "0";
+            if (0 != (table() & (1ull << i))) out << "1"; else out << "0";
         }    
         return out;
     }
diff --git a/src/sat/sat_cutset.h b/src/sat/sat_cutset.h
index ec2675ce1..ec189e958 100644
--- a/src/sat/sat_cutset.h
+++ b/src/sat/sat_cutset.h
@@ -25,11 +25,17 @@ namespace sat {
         unsigned m_filter;
         unsigned m_size;
         unsigned m_elems[4];
-    public:
         uint64_t m_table;
-        cut(): m_filter(0), m_size(0), m_table(0) {}
+        mutable uint64_t m_dont_care;
 
-        cut(unsigned id): m_filter(1u << (id & 0x1F)), m_size(1), m_table(2) { m_elems[0] = id; }
+        uint64_t table_mask() const { return (1ull << (1ull << m_size)) - 1ull; }
+
+    public:
+        cut(): m_filter(0), m_size(0), m_table(0), m_dont_care(0) {}
+
+        cut(unsigned id): m_filter(1u << (id & 0x1F)), m_size(1), m_table(2), m_dont_care(0) { 
+            m_elems[0] = id; 
+        }
 
         cut(cut const& other) {
             *this = other;
@@ -39,6 +45,7 @@ namespace sat {
             m_filter = other.m_filter;
             m_size = other.m_size;
             m_table = other.m_table;
+            m_dont_care = other.m_dont_care;
             for (unsigned i = 0; i < m_size; ++i) m_elems[i] = other.m_elems[i];
             return *this;
         }
@@ -62,11 +69,14 @@ namespace sat {
         }
         void sort();
         void negate() { set_table(~m_table); }
-        uint64_t table_mask() const { return (1ull << (1ull << m_size)) - 1ull; }
         void set_table(uint64_t t) { m_table = t & table_mask(); }
+        uint64_t table() const { return (m_table | m_dont_care) & table_mask(); }
 
-        bool is_true()  const { return 0 == (table_mask() & ~m_table); }
-        bool is_false() const { return 0 == (table_mask() &  m_table); }
+        uint64_t dont_care() const { return m_dont_care; }
+        void add_dont_care(uint64_t t) const { m_dont_care |= t; }
+
+        bool is_true()  const { return 0 == (table_mask() & ~table()); }
+        bool is_false() const { return 0 == (table_mask() & ~m_dont_care & m_table); }
 
         bool operator==(cut const& other) const;
         bool operator!=(cut const& other) const { return !(*this == other); }
@@ -157,8 +167,6 @@ namespace sat {
         }
         void evict(on_update_t& on_del, unsigned idx);
 
-        void replace(on_update_t& on_add, on_update_t& on_del, cut const& src, cut const& dst);
-
         std::ostream& display(std::ostream& out) const;
     };