diff --git a/src/math/bigfix/Hacl_Bignum.c b/src/math/bigfix/Hacl_Bignum.c
index 54a282839..9dab783f8 100644
--- a/src/math/bigfix/Hacl_Bignum.c
+++ b/src/math/bigfix/Hacl_Bignum.c
@@ -317,6 +317,7 @@ static inline void bn_sqr_u32(uint32_t aLen, uint32_t *a, uint32_t *res)
     res[i0 + i0] = r;
   }
   uint32_t c0 = Hacl_Bignum_Addition_bn_add_eq_len_u32(resLen, res, res, res);
+  (void)c0;
   KRML_CHECK_SIZE(sizeof (uint32_t), resLen);
   uint32_t *tmp = alloca(resLen * sizeof (uint32_t));
   memset(tmp, 0U, resLen * sizeof (uint32_t));
@@ -329,6 +330,7 @@ static inline void bn_sqr_u32(uint32_t aLen, uint32_t *a, uint32_t *res)
     tmp[(uint32_t)2U * i + (uint32_t)1U] = hi;
   }
   uint32_t c1 = Hacl_Bignum_Addition_bn_add_eq_len_u32(resLen, res, tmp, res);
+  (void)c1;
 }
 
 static inline void bn_sqr_u64(uint32_t aLen, uint64_t *a, uint64_t *res)
@@ -366,6 +368,7 @@ static inline void bn_sqr_u64(uint32_t aLen, uint64_t *a, uint64_t *res)
     res[i0 + i0] = r;
   }
   uint64_t c0 = Hacl_Bignum_Addition_bn_add_eq_len_u64(resLen, res, res, res);
+  (void)c0;
   KRML_CHECK_SIZE(sizeof (uint64_t), resLen);
   uint64_t *tmp = alloca(resLen * sizeof (uint64_t));
   memset(tmp, 0U, resLen * sizeof (uint64_t));
@@ -378,6 +381,7 @@ static inline void bn_sqr_u64(uint32_t aLen, uint64_t *a, uint64_t *res)
     tmp[(uint32_t)2U * i + (uint32_t)1U] = hi;
   }
   uint64_t c1 = Hacl_Bignum_Addition_bn_add_eq_len_u64(resLen, res, tmp, res);
+  (void)c1;
 }
 
 void
@@ -720,6 +724,7 @@ Hacl_Bignum_Karatsuba_bn_karatsuba_sqr_uint64(
   uint64_t *tmp_ = tmp + aLen;
   uint64_t c0 = Hacl_Bignum_Addition_bn_sub_eq_len_u64(len2, a0, a1, tmp_);
   uint64_t c1 = Hacl_Bignum_Addition_bn_sub_eq_len_u64(len2, a1, a0, t0);
+  (void)c1;
   for (uint32_t i = (uint32_t)0U; i < len2; i++)
   {
     uint64_t *os = t0;
@@ -727,6 +732,7 @@ Hacl_Bignum_Karatsuba_bn_karatsuba_sqr_uint64(
     os[i] = x;
   }
   uint64_t c00 = c0;
+  (void)c00;
   uint64_t *t23 = tmp + aLen;
   uint64_t *tmp1 = tmp + aLen + aLen;
   Hacl_Bignum_Karatsuba_bn_karatsuba_sqr_uint64(len2, t0, tmp1, t23);
@@ -1428,6 +1434,7 @@ bn_almost_mont_reduction_u32(
   uint32_t *tmp = alloca(len * sizeof (uint32_t));
   memset(tmp, 0U, len * sizeof (uint32_t));
   uint32_t c1 = Hacl_Bignum_Addition_bn_sub_eq_len_u32(len, res, n, tmp);
+  (void)c1;
   uint32_t m = (uint32_t)0U - c00;
   for (uint32_t i = (uint32_t)0U; i < len; i++)
   {
@@ -1524,6 +1531,7 @@ bn_almost_mont_reduction_u64(
   uint64_t *tmp = alloca(len * sizeof (uint64_t));
   memset(tmp, 0U, len * sizeof (uint64_t));
   uint64_t c1 = Hacl_Bignum_Addition_bn_sub_eq_len_u64(len, res, n, tmp);
+  (void)c1;
   uint64_t m = (uint64_t)0U - c00;
   for (uint32_t i = (uint32_t)0U; i < len; i++)
   {
diff --git a/src/math/bigfix/Hacl_Bignum256.c b/src/math/bigfix/Hacl_Bignum256.c
index 6894f8bd8..7eee57ccd 100644
--- a/src/math/bigfix/Hacl_Bignum256.c
+++ b/src/math/bigfix/Hacl_Bignum256.c
@@ -513,6 +513,7 @@ static inline void amont_sqr(uint64_t *n, uint64_t nInv_u64, uint64_t *aM, uint6
     tmp[(uint32_t)2U * i + (uint32_t)1U] = hi;
   }
   uint64_t c1 = Hacl_Bignum_Addition_bn_add_eq_len_u64(resLen, c, tmp, c);
+  (void)c1;
   areduction(n, nInv_u64, c, resM);
 }
 
@@ -559,6 +560,7 @@ bn_slow_precomp(uint64_t *n, uint64_t mu, uint64_t *r2, uint64_t *a, uint64_t *r
   uint64_t c00 = c0;
   uint64_t tmp[4U] = { 0U };
   uint64_t c1 = Hacl_Bignum256_sub(a_mod, n, tmp);
+  (void)c1;
   uint64_t m = (uint64_t)0U - c00;
   for (uint32_t i = (uint32_t)0U; i < (uint32_t)4U; i++)
   {
@@ -1132,6 +1134,7 @@ bool Hacl_Bignum256_mod_inv_prime_vartime(uint64_t *n, uint64_t *a, uint64_t *re
     uint64_t n2[4U] = { 0U };
     uint64_t c0 = Lib_IntTypes_Intrinsics_sub_borrow_u64((uint64_t)0U, n[0U], (uint64_t)2U, n2);
     uint64_t c1;
+    (void)c1;
     if ((uint32_t)1U < (uint32_t)4U)
     {
       uint32_t rLen = (uint32_t)3U;
@@ -1334,6 +1337,7 @@ Hacl_Bignum256_mod_inv_prime_vartime_precomp(
   uint64_t n2[4U] = { 0U };
   uint64_t c0 = Lib_IntTypes_Intrinsics_sub_borrow_u64((uint64_t)0U, k1.n[0U], (uint64_t)2U, n2);
   uint64_t c1;
+  (void)c1;
   if ((uint32_t)1U < (uint32_t)4U)
   {
     uint32_t rLen = (uint32_t)3U;
diff --git a/src/math/polysat/fixplex.h b/src/math/polysat/fixplex.h
index a2c5450bf..f6af50ccd 100644
--- a/src/math/polysat/fixplex.h
+++ b/src/math/polysat/fixplex.h
@@ -30,6 +30,8 @@ Author:
 #include "util/ref.h"
 
 inline rational to_rational(uint64_t n) { return rational(n, rational::ui64()); }
+inline unsigned trailing_zeros(unsigned short n) { return trailing_zeros((uint32_t)n); }
+inline unsigned trailing_zeros(unsigned char n) { return trailing_zeros((uint32_t)n); }
 
 namespace polysat {
 
@@ -40,6 +42,8 @@ namespace polysat {
         virtual lbool make_feasible() = 0;
         virtual void add_row(var_t base, unsigned num_vars, var_t const* vars, rational const* coeffs) = 0;
         virtual void del_row(var_t base_var) = 0;
+        virtual void push() = 0;
+        virtual void pop(unsigned n) = 0;
         virtual std::ostream& display(std::ostream& out) const = 0;
         virtual void collect_statistics(::statistics & st) const = 0;
         virtual void set_bounds(var_t v, rational const& lo, rational const& hi, unsigned dep) = 0;        
@@ -50,6 +54,7 @@ namespace polysat {
         virtual void add_lt(var_t v, var_t w, unsigned dep) = 0;
         virtual void restore_ineq() = 0;
         virtual unsigned_vector const& get_unsat_core() const = 0;
+
     };
 
 
@@ -95,14 +100,6 @@ namespace polysat {
             S_DEFAULT
         };
 
-#if 0
-        struct dep_config {
-            static const bool ref_count = true;
-            typedef unsigned value;
-        };
-        typedef dependency_manager<dep_config> dep_manager;
-#endif
-
         struct var_info : public mod_interval<numeral> {
             unsigned      m_base2row:29;
             unsigned      m_is_base:1;
@@ -156,6 +153,13 @@ namespace polysat {
                 v(v), w(w), strict(s), dep(dep) {}
         };
 
+        enum trail_i {
+            inc_level_i,
+            set_bound_i,
+            add_ineq_i,
+            add_row_i
+        };
+
         static const var_t null_var = UINT_MAX;
         reslimit&                   m_limit;
         mutable manager             m;
@@ -175,6 +179,8 @@ namespace polysat {
         stats                       m_stats;
         vector<stashed_bound>       m_stashed_bounds;
         u_dependency_manager        m_deps;
+        svector<trail_i>            m_trail;
+        svector<var_t>              m_row_trail;
         map<numeral, fix_entry, typename manager::hash, typename manager::eq> m_value2fixed_var;
 
         // inequalities
@@ -192,6 +198,9 @@ namespace polysat {
 
         ~fixplex() override;
 
+        void push() override;
+        void pop(unsigned n) override;
+
         lbool make_feasible() override;
         void add_row(var_t base, unsigned num_vars, var_t const* vars, rational const* coeffs) override;
         std::ostream& display(std::ostream& out) const override;
@@ -206,6 +215,7 @@ namespace polysat {
         virtual void restore_ineq() override;
 
         void set_bounds(var_t v, numeral const& lo, numeral const& hi, unsigned dep);
+        void update_bounds(var_t v, numeral const& l, numeral const& h, u_dependency* dep);
         void unset_bounds(var_t v) { m_vars[v].set_free(); }
 
 
@@ -244,8 +254,11 @@ namespace polysat {
         lbool propagate_bounds(row const& r);
         lbool propagate_bounds(ineq const& i);
         lbool new_bound(row const& r, var_t x, mod_interval<numeral> const& range);
-        lbool new_bound(ineq const& i, var_t x, numeral const& lo, numeral const& hi);
-        lbool conflict_bound(ineq const& i);
+        lbool new_bound(ineq const& i, var_t x, numeral const& lo, numeral const& hi, u_dependency* a = nullptr, u_dependency* b = nullptr);
+        lbool conflict(ineq const& i, u_dependency* a = nullptr, u_dependency* b = nullptr);
+        lbool conflict(u_dependency* a);
+        lbool conflict(u_dependency* a, u_dependency* b) { return conflict(m_deps.mk_join(a, b)); }
+        u_dependency* row2dep(row const& r);
         void pivot(var_t x_i, var_t x_j, numeral const& b, numeral const& value);
         numeral value2delta(var_t v, numeral const& new_value) const;
         numeral value2error(var_t v, numeral const& new_value) const;
@@ -279,6 +292,8 @@ namespace polysat {
         void set_infeasible_base(var_t v);
         void set_infeasible_bounds(var_t v);
 
+        u_dependency* mk_leaf(unsigned dep) { return UINT_MAX == dep ? nullptr : m_deps.mk_leaf(dep); }
+
         // facilities for handling inequalities
         void add_ineq(var_t v, var_t w, unsigned dep, bool strict);
         void touch_var(var_t x);
diff --git a/src/math/polysat/fixplex_def.h b/src/math/polysat/fixplex_def.h
index e335bc204..722621189 100644
--- a/src/math/polysat/fixplex_def.h
+++ b/src/math/polysat/fixplex_def.h
@@ -72,6 +72,37 @@ namespace polysat {
         reset();
     }
 
+    template<typename Ext>
+    void fixplex<Ext>::push() {
+        m_trail.push_back(trail_i::inc_level_i);
+        m_deps.push_scope();
+    }
+
+    template<typename Ext>
+    void fixplex<Ext>::pop(unsigned n) {
+        m_deps.pop_scope(n);
+        while (n > 0) {
+            switch (m_trail.back()) {
+            case trail_i::inc_level_i:                
+                --n;
+                break;
+            case trail_i::set_bound_i: 
+                restore_bound();
+                break;            
+            case trail_i::add_row_i: 
+                del_row(m_row_trail.back());
+                m_row_trail.pop_back();
+                break;            
+            case trail_i::add_ineq_i: 
+                restore_ineq();
+                break;            
+            default:
+                UNREACHABLE();
+            }
+            m_trail.pop_back();
+        }
+    }
+
     template<typename Ext>
     void fixplex<Ext>::ensure_var(var_t v) {
         while (v >= m_vars.size()) {
@@ -173,6 +204,8 @@ namespace polysat {
             ++m_stats.m_num_approx;
         SASSERT(well_formed_row(r));
         SASSERT(well_formed());
+        m_trail.push_back(trail_i::add_row_i);
+        m_row_trail.push_back(base_var);
     }
 
     template<typename Ext>
@@ -486,13 +519,7 @@ namespace polysat {
      */
     template<typename Ext>
     void fixplex<Ext>::set_bounds(var_t v, numeral const& l, numeral const& h, unsigned dep) {
-        auto lo0 = m_vars[v].lo;
-        auto hi0 = m_vars[v].hi;
-        m_vars[v] &= mod_interval(l, h);
-        if (lo0 != m_vars[v].lo)
-            m_vars[v].m_lo_dep = nullptr; // TODO set_atom(dep);
-        if (hi0 != m_vars[v].hi)
-            m_vars[v].m_hi_dep = nullptr; // TODO .set_atom(dep);
+        update_bounds(v, l, h, mk_leaf(dep));
         if (in_bounds(v))
             return;
         if (is_base(v))
@@ -501,18 +528,29 @@ namespace polysat {
             update_value(v, value2delta(v, value(v)));
     }
 
+    template<typename Ext>
+    void fixplex<Ext>::update_bounds(var_t v, numeral const& l, numeral const& h, u_dependency* dep) {
+        auto lo0 = m_vars[v].lo;
+        auto hi0 = m_vars[v].hi;
+        m_stashed_bounds.push_back(stashed_bound(v, m_vars[v]));
+        m_trail.push_back(trail_i::set_bound_i);
+        m_vars[v] &= mod_interval(l, h);
+        if (lo0 != m_vars[v].lo)
+            m_vars[v].m_lo_dep = dep;
+        if (hi0 != m_vars[v].hi)
+            m_vars[v].m_hi_dep = dep;
+    }
+
     template<typename Ext>
     void fixplex<Ext>::set_bounds(var_t v, rational const& _lo, rational const& _hi, unsigned dep) {
         numeral lo = m.from_rational(_lo);
         numeral hi = m.from_rational(_hi);
-        m_stashed_bounds.push_back(stashed_bound(v, m_vars[v]));
         set_bounds(v, lo, hi, dep);
     }
 
     template<typename Ext>
     void fixplex<Ext>::set_value(var_t v, rational const& _val, unsigned dep) {
         numeral val = m.from_rational(_val);
-        m_stashed_bounds.push_back(stashed_bound(v, m_vars[v]));
         set_bounds(v, val, val + 1, dep);
     }
 
@@ -524,24 +562,21 @@ namespace polysat {
     template<typename Ext>
     void fixplex<Ext>::restore_bound() {
         auto& b = m_stashed_bounds.back();
-        auto* lo = m_vars[b.m_var].m_lo_dep;
-        auto* hi = m_vars[b.m_var].m_hi_dep;
         m_vars[b.m_var].lo = b.lo;
         m_vars[b.m_var].hi = b.hi;
         m_vars[b.m_var].m_lo_dep = b.m_lo_dep;
         m_vars[b.m_var].m_hi_dep = b.m_hi_dep;
-//        m_deps.dec_ref(lo);
-//        m_deps.dec_ref(hi);
         m_stashed_bounds.pop_back();
     }
 
     template<typename Ext>
     void fixplex<Ext>::add_ineq(var_t v, var_t w, unsigned dep, bool strict) {
-        unsigned idx = m_ineqs.size();
+        unsigned idx = m_ineqs.size();        
         m_var2ineqs.reserve(std::max(v, w) + 1);
         m_var2ineqs[v].push_back(idx);
         m_var2ineqs[w].push_back(idx);
         m_ineqs_to_check.push_back(idx);
+        m_trail.push_back(trail_i::add_ineq_i);
         m_ineqs.push_back(ineq(v, w, dep, strict));
     }
 
@@ -1126,50 +1161,64 @@ namespace polysat {
         var_t v = i.v, w = i.w;
         bool s = i.strict;
         if (s && lo(v) + 1 == 0)
-            return conflict_bound(i);
+            return conflict(i, m_vars[v].m_lo_dep);
         else if (s && hi(w) == 0)
-            return conflict_bound(i);
+            return conflict(i, m_vars[v].m_hi_dep);
         else if (s && lo(v) >= hi(w))
-            return conflict_bound(i);
+            return conflict(i, m_vars[v].m_lo_dep, m_vars[w].m_hi_dep);
         else if (!s && lo(v) > hi(w))
-            return conflict_bound(i);
+            return conflict(i, m_vars[v].m_lo_dep, m_vars[w].m_hi_dep);
         else if (s && hi(v) >= hi(w)) {
             SASSERT(lo(v) < hi(w));
             SASSERT(hi(w) != 0);
-            return new_bound(i, v, lo(v), hi(w) - 1);
+            return new_bound(i, v, lo(v), hi(w) - 1, m_vars[v].m_hi_dep, m_vars[w].m_hi_dep);
         }
         else if (s && lo(v) >= lo(w)) {
             SASSERT(lo(v) + 1 != 0);
             SASSERT(hi(w) > lo(v));
-            return new_bound(i, w, lo(v) + 1, hi(w));
+            return new_bound(i, w, lo(v) + 1, hi(w), m_vars[v].m_lo_dep, m_vars[w].m_lo_dep);
         }
         else if (!s && hi(v) > hi(w)) {
             SASSERT(lo(v) <= hi(w));
-            return new_bound(i, v, lo(v), hi(w));
+            return new_bound(i, v, lo(v), hi(w), m_vars[v].m_hi_dep, m_vars[w].m_hi_dep);
         }
         else if (!s && lo(v) > lo(w)) {
             SASSERT(lo(v) <= hi(w));
-            return new_bound(i, w, lo(v), hi(w));
+            return new_bound(i, w, lo(v), hi(w), m_vars[v].m_lo_dep, m_vars[w].m_lo_dep);
         }
         return l_true;
     }
 
     template<typename Ext>
-    lbool fixplex<Ext>::conflict_bound(ineq const& i) {
-        NOT_IMPLEMENTED_YET();
+    lbool fixplex<Ext>::conflict(ineq const& i, u_dependency* a, u_dependency* b) {
+        return conflict(a, m_deps.mk_join(mk_leaf(i.dep), b));
+    }
+
+    template<typename Ext>
+    lbool fixplex<Ext>::conflict(u_dependency* a) {
+        m_unsat_core.reset();
+        m_deps.linearize(a, m_unsat_core);
         return l_false;
     }
 
     template<typename Ext>
-    lbool fixplex<Ext>::new_bound(ineq const& i, var_t x, numeral const& l, numeral const& h) {
-        mod_interval<numeral> r(l, h);
-        bool was_fixed = lo(x) + 1 == hi(x);
-        m_vars[x] &= r;
-        if (m_vars[x].is_empty()) {
-            // TODO
-            IF_VERBOSE(0, verbose_stream() << "infeasible\n");
-            return l_false;
+    u_dependency* fixplex<Ext>::row2dep(row const& r) {
+        u_dependency* d = nullptr;
+        for (auto const& e : M.row_entries(r)) {
+            var_t v = e.var();
+            d = m_deps.mk_join(m_vars[v].m_lo_dep, d);
+            d = m_deps.mk_join(m_vars[v].m_hi_dep, d);
         }
+        return d;
+    }
+
+    template<typename Ext>
+    lbool fixplex<Ext>::new_bound(ineq const& i, var_t x, numeral const& l, numeral const& h, u_dependency* a, u_dependency* b) {
+        bool was_fixed = lo(x) + 1 == hi(x);
+        u_dependency* dep = m_deps.mk_join(mk_leaf(i.dep), m_deps.mk_join(a, b));
+        update_bounds(x, l, h, dep);
+        if (m_vars[x].is_empty())
+            return conflict(m_vars[x].m_lo_dep, m_vars[x].m_hi_dep);
         else if (!was_fixed && lo(x) + 1 == hi(x)) {
             // TBD: track based on inequality not row
             // fixed_var_eh(r, x);
@@ -1182,12 +1231,10 @@ namespace polysat {
         if (range.is_free())
             return l_true;
         bool was_fixed = lo(x) + 1 == hi(x);
-        m_vars[x] &= range;
+        update_bounds(x, range.lo, range.hi, row2dep(r));
         IF_VERBOSE(0, verbose_stream() << "new-bound v" << x << " " << m_vars[x] << "\n");
-        if (m_vars[x].is_empty()) {
-            IF_VERBOSE(0, verbose_stream() << "infeasible\n");
-            return l_false;
-        }
+        if (m_vars[x].is_empty()) 
+            return conflict(m_vars[x].m_lo_dep, m_vars[x].m_hi_dep);
         else if (!was_fixed && lo(x) + 1 == hi(x)) 
             fixed_var_eh(r, x);
         return l_true;
diff --git a/src/math/polysat/linear_solver.cpp b/src/math/polysat/linear_solver.cpp
index 699a28d31..535d9c670 100644
--- a/src/math/polysat/linear_solver.cpp
+++ b/src/math/polysat/linear_solver.cpp
@@ -22,9 +22,13 @@ namespace polysat {
 
     void linear_solver::push() {
         m_trail.push_back(trail_i::inc_level_i);
+        for (auto* f : m_fix_ptr)
+            f->push();
     }
 
     void linear_solver::pop(unsigned n) {
+        for (auto* f : m_fix_ptr)
+            f->pop(n);
         while (n > 0) {
             switch (m_trail.back()) {
             case trail_i::inc_level_i:
@@ -43,24 +47,6 @@ namespace polysat {
                 m_monomials.pop_back();
                 break;
             }
-            case trail_i::set_bound_i: {
-                auto [v, sz] = m_rows.back();
-                sz2fixplex(sz).restore_bound();
-                m_rows.pop_back();
-                break;
-            }
-            case trail_i::add_row_i: {
-                auto [v, sz] = m_rows.back();
-                sz2fixplex(sz).del_row(v);
-                m_rows.pop_back();
-                break;
-            }
-            case trail_i::add_ineq_i: {
-                auto [v, sz] = m_rows.back();
-                sz2fixplex(sz).restore_ineq();
-                m_rows.pop_back();
-                break;
-            }
             case trail_i::set_active_i: 
                 m_active.pop_back();
                 break;            
@@ -73,10 +59,16 @@ namespace polysat {
         m_unsat_f = nullptr;
     }
     
-    fixplex_base& linear_solver::sz2fixplex(unsigned sz) { 
+    fixplex_base* linear_solver::sz2fixplex(unsigned sz) { 
         fixplex_base* b = m_fix.get(sz, nullptr);
         if (!b) {
             switch (sz) {
+            case 8:
+                b = alloc(fixplex<generic_uint_ext<unsigned char>>, s.m_lim);
+                break;
+            case 16:
+                b = alloc(fixplex<generic_uint_ext<unsigned short>>, s.m_lim);
+                break;
             case 32:
                 b = alloc(fixplex<generic_uint_ext<unsigned>>, s.m_lim);
                 break;
@@ -93,9 +85,11 @@ namespace polysat {
                 NOT_IMPLEMENTED_YET();
                 break;
             }
+            if (b)
+                m_fix_ptr.push_back(b);
             m_fix.set(sz, b);
         }
-        return *b;
+        return b;
     }  
 
 
@@ -107,9 +101,9 @@ namespace polysat {
         var_t v = fresh_var(sz);
         m_vars.push_back(v);
         m_coeffs.push_back(rational::power_of_two(sz) - 1);
-        sz2fixplex(sz).add_row(v, m_vars.size(), m_vars.data(), m_coeffs.data());
-        m_rows.push_back(std::make_pair(v, sz));
-        m_trail.push_back(trail_i::add_row_i);
+        auto* f = sz2fixplex(sz);
+        if (f)
+            f->add_row(v, m_vars.size(), m_vars.data(), m_coeffs.data());
         return v;
     }
     
@@ -135,15 +129,15 @@ namespace polysat {
         unsigned c_dep = constraint_idx2dep(m_active.size() - 1);
         var_t v = m_bool_var2row[c.bvar()].first;
         unsigned sz = c.p().power_of_2();
-        auto& fp = sz2fixplex(sz);            
-        m_trail.push_back(trail_i::set_bound_i);
-        m_rows.push_back(std::make_pair(v, sz));
+        auto* fp = sz2fixplex(sz);    
+        if (!fp)
+            return;
         rational z(0), o(1);
         SASSERT(!c.is_undef());
         if (is_positive) 
-            fp.set_bounds(v, z, z, c_dep);
+            fp->set_bounds(v, z, z, c_dep);
         else 
-            fp.set_bounds(v, o, z, c_dep);
+            fp->set_bounds(v, o, z, c_dep);
     }
 
     //
@@ -162,44 +156,40 @@ namespace polysat {
     void linear_solver::assert_le(bool is_positive, ule_constraint& c) {
         auto [v, w] = m_bool_var2row[c.bvar()];
         unsigned sz = c.lhs().power_of_2();
-        auto& fp = sz2fixplex(sz);     
+        auto* fp = sz2fixplex(sz);     
+        if (!fp)
+            return;
         unsigned c_dep = constraint_idx2dep(m_active.size() - 1);
         rational z(0);
         if (c.rhs().is_val()) {
             bool is_max_value = false; 
             if (is_positive) 
                 // v <= rhs
-                fp.set_bounds(v, z, c.rhs().val(), c_dep);                 
+                fp->set_bounds(v, z, c.rhs().val(), c_dep);                 
             else if (is_max_value) 
                 throw default_exception("conflict not implemented");
             else 
                 // rhs < v
-                fp.set_bounds(v, c.rhs().val() + 1, z, c_dep);
-            m_trail.push_back(trail_i::set_bound_i);
-            m_rows.push_back(std::make_pair(v, sz));
+                fp->set_bounds(v, c.rhs().val() + 1, z, c_dep);
             return;
         }
 
         if (c.lhs().is_val()) {
             if (is_positive)
                 // w >= lhs 
-                fp.set_bounds(w, c.lhs().val(), z, c_dep);
+                fp->set_bounds(w, c.lhs().val(), z, c_dep);
             else if (c.lhs().val() == 0)
                 throw default_exception("conflict not implemented");
             else 
                 // w < lhs 
-                fp.set_bounds(w, z, c.lhs().val() - 1, c_dep);
-            m_trail.push_back(trail_i::set_bound_i);
-            m_rows.push_back(std::make_pair(w, sz));
+                fp->set_bounds(w, z, c.lhs().val() - 1, c_dep);
             return;
         }
 
         if (is_positive) 
-            fp.add_le(v, w, c_dep);
+            fp->add_le(v, w, c_dep);
         else 
-            fp.add_lt(w, v, c_dep);
-        m_trail.push_back(trail_i::add_ineq_i);
-        m_rows.push_back(std::make_pair(v, sz));
+            fp->add_lt(w, v, c_dep);
     }
 
 
@@ -273,20 +263,20 @@ namespace polysat {
 
     void linear_solver::set_value(pvar v, rational const& value, unsigned dep) {
         unsigned sz = s.size(v);
-        auto& fp = sz2fixplex(sz);
+        auto* fp = sz2fixplex(sz);
+        if (!fp)
+            return;
         var_t w = pvar2var(sz, v);
-        m_trail.push_back(trail_i::set_bound_i);
-        m_rows.push_back(std::make_pair(w, sz));
-        fp.set_value(w, value, external_dep2dep(dep));
+        fp->set_value(w, value, external_dep2dep(dep));
     }
 
     void linear_solver::set_bound(pvar v, rational const& lo, rational const& hi, unsigned dep) {
         unsigned sz = s.size(v);
-        auto& fp = sz2fixplex(sz);
+        auto* fp = sz2fixplex(sz);
+        if (!fp)
+            return;
         var_t w = pvar2var(sz, v);
-        m_trail.push_back(trail_i::set_bound_i);
-        m_rows.push_back(std::make_pair(w, sz));
-        fp.set_bounds(w, lo, hi, external_dep2dep(dep));
+        fp->set_bounds(w, lo, hi, external_dep2dep(dep));
     }
     
     /** 
@@ -325,7 +315,10 @@ namespace polysat {
     // current value assigned to (linear) variable according to tableau.
     rational linear_solver::value(pvar v) { 
         unsigned sz = s.size(v);
-        return sz2fixplex(sz).get_value(pvar2var(sz, v));
+        auto* fp = sz2fixplex(sz);
+        if (!fp)
+            return rational::zero();
+        return fp->get_value(pvar2var(sz, v));
     }
     
 };
diff --git a/src/math/polysat/linear_solver.h b/src/math/polysat/linear_solver.h
index 8472a0721..88602a4e3 100644
--- a/src/math/polysat/linear_solver.h
+++ b/src/math/polysat/linear_solver.h
@@ -41,7 +41,6 @@ namespace polysat {
             inc_level_i,
             add_var_i,
             add_mono_i,
-            set_bound_i,
             add_ineq_i,
             add_row_i,
             set_active_i
@@ -78,6 +77,7 @@ namespace polysat {
 
         solver&                  s;
         scoped_ptr_vector<fixplex_base> m_fix;
+        ptr_vector<fixplex_base> m_fix_ptr;
         svector<trail_i>         m_trail;
         svector<std::pair<var_t, unsigned>> m_rows; 
         unsigned_vector          m_var2ext;
@@ -94,7 +94,7 @@ namespace polysat {
         svector<mono_info>       m_monomials;
         fixplex_base*            m_unsat_f = nullptr;
 
-        fixplex_base& sz2fixplex(unsigned sz);
+        fixplex_base* sz2fixplex(unsigned sz);
 
         void linearize(pdd const& p);
         var_t fresh_var(unsigned sz);