diff --git a/src/math/interval/mod_interval.h b/src/math/interval/mod_interval.h
index 88dfff485..50b6efe94 100644
--- a/src/math/interval/mod_interval.h
+++ b/src/math/interval/mod_interval.h
@@ -59,6 +59,7 @@ public:
     bool is_empty() const { return emp; }
     bool is_singleton() const { return !is_empty() && (lo + 1 == hi || (hi == 0 && is_max(lo))); }
     bool contains(Numeral const& n) const;
+    bool contains(mod_interval const& other) const;
     virtual bool is_max(Numeral const& n) const { return (Numeral)(n + 1) == 0; }
 
     void set_free() { lo = hi = 0; emp = false; }
diff --git a/src/math/interval/mod_interval_def.h b/src/math/interval/mod_interval_def.h
index 06b12b56c..cc5a78d1b 100644
--- a/src/math/interval/mod_interval_def.h
+++ b/src/math/interval/mod_interval_def.h
@@ -32,6 +32,27 @@ bool mod_interval<Numeral>::contains(Numeral const& n) const {
         return lo <= n || n < hi;
 }
 
+template<typename Numeral>
+bool mod_interval<Numeral>::contains(mod_interval const& other) const {
+    if (is_empty())
+        return other.is_empty();
+    if (is_free())
+        return true;
+    if (hi == 0)
+        return lo <= other.lo && (other.lo < other.hi || other.hi == 0);
+    if (lo < hi)
+        return lo <= other.lo && other.hi <= hi;
+    if (other.lo < other.hi && other.hi <= hi)
+        return true;
+    if (other.lo < other.hi && lo <= other.lo)
+        return true;
+    if (other.hi == 0)
+        return lo <= other.lo;
+    SASSERT(other.hi < other.lo && other.hi != 0);
+    SASSERT(hi < lo && hi != 0);
+    return lo <= other.lo && other.hi <= hi;
+}
+
 template<typename Numeral>
 mod_interval<Numeral> mod_interval<Numeral>::operator+(mod_interval<Numeral> const& other) const {
     if (is_empty())
diff --git a/src/math/polysat/fixplex.h b/src/math/polysat/fixplex.h
index 34571b897..dd5dfe57a 100644
--- a/src/math/polysat/fixplex.h
+++ b/src/math/polysat/fixplex.h
@@ -29,6 +29,7 @@ Author:
 #include "util/dependency.h"
 #include "util/ref.h"
 #include "util/params.h"
+#include "util/union_find.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); }
@@ -183,8 +184,7 @@ namespace polysat {
         var_heap                    m_to_patch;
         vector<var_info>            m_vars;
         vector<row_info>            m_rows;
-        vector<var_eq>              m_var_eqs;
-        vector<numeral>             m_fixed_vals;
+
         bool                        m_bland = false ;
         unsigned                    m_blands_rule_threshold = 1000;
         unsigned                    m_num_repeated = 0;
@@ -198,7 +198,14 @@ namespace polysat {
         u_dependency_manager        m_deps;
         svector<trail_i>            m_trail;
         svector<var_t>              m_row_trail;
+
+        // euqality propagation
+        union_find_default_ctx      m_union_find_ctx;
+        union_find<>                m_union_find;
+        vector<var_eq>              m_var_eqs;
+        vector<numeral>             m_fixed_vals;
         map<numeral, fix_entry, typename manager::hash, typename manager::eq> m_value2fixed_var;
+        uint_set                    m_eq_rows;
 
         // inequalities
         svector<ineq>               m_ineqs;
@@ -206,11 +213,15 @@ namespace polysat {
         uint_set                    m_touched_vars;
         vector<unsigned_vector>     m_var2ineqs;
 
+        // bound propagation
+        uint_set                    m_bound_rows;
+
     public:
         fixplex(params_ref const& p, reslimit& lim):
             m_limit(lim),
             M(m),
-            m_to_patch(1024) {
+            m_to_patch(1024),
+            m_union_find(m_union_find_ctx) {
             updt_params(p);
         }
 
@@ -249,7 +260,6 @@ namespace polysat {
         svector<std::pair<unsigned, unsigned>> stack;
         uint_set on_stack;
         lbool propagate_ineqs(unsigned idx);
-        void propagate_eqs();
         vector<var_eq> const& var_eqs() const { return m_var_eqs; }
 
         void add_row(var_t base, unsigned num_vars, var_t const* vars, numeral const* coeffs);
@@ -266,6 +276,9 @@ namespace polysat {
 
         bool patch();
         bool propagate();
+        bool propagate_ineqs();
+        bool propagate_row_eqs();
+        bool propagate_row_bounds();
         bool is_satisfied();
 
         var_t select_smallest_var() { return m_to_patch.empty()?null_var:m_to_patch.erase_min(); }
@@ -276,6 +289,8 @@ namespace polysat {
         void lookahead_eq(row const& r1, numeral const& cx, var_t x, numeral const& cy, var_t y);
         void get_offset_eqs(row const& r);
         void fixed_var_eh(u_dependency* dep, var_t x);
+        var_t find(var_t x) { return m_union_find.find(x); }
+        void merge(var_t x, var_t y) { m_union_find.merge(x, y); }
         void eq_eh(var_t x, var_t y, u_dependency* dep);
         bool propagate_row(row const& r);
         bool propagate_ineq(ineq const& i);
diff --git a/src/math/polysat/fixplex_def.h b/src/math/polysat/fixplex_def.h
index 6eaf17b03..1223fe783 100644
--- a/src/math/polysat/fixplex_def.h
+++ b/src/math/polysat/fixplex_def.h
@@ -91,11 +91,13 @@ namespace polysat {
     void fixplex<Ext>::push() {
         m_trail.push_back(trail_i::inc_level_i);
         m_deps.push_scope();
+        m_union_find_ctx.get_trail_stack().push_scope();
     }
 
     template<typename Ext>
     void fixplex<Ext>::pop(unsigned n) {
         m_deps.pop_scope(n);
+        m_union_find_ctx.get_trail_stack().pop_scope(n);
         while (n > 0) {
             switch (m_trail.back()) {
             case trail_i::inc_level_i:
@@ -135,6 +137,7 @@ namespace polysat {
         while (v >= m_vars.size()) {
             M.ensure_var(m_vars.size());
             m_vars.push_back(var_info());
+            m_union_find.mk_var();
         }
         if (m_to_patch.get_bounds() <= v)
             m_to_patch.set_bounds(2 * v + 1);
@@ -242,6 +245,8 @@ namespace polysat {
         SASSERT(well_formed());
         m_trail.push_back(trail_i::add_row_i);
         m_row_trail.push_back(base_var);
+        m_eq_rows.insert(r.id());
+        m_bound_rows.insert(r.id());
     }
 
     template<typename Ext>
@@ -286,6 +291,8 @@ namespace polysat {
         m_rows[r.id()].m_base = null_var;
         m_non_integral.remove(r.id());
         M.del(r);
+        m_eq_rows.remove(r.id());
+        m_bound_rows.remove(r.id());
         SASSERT(M.col_begin(var) == M.col_end(var));
         SASSERT(well_formed());
     }
@@ -671,11 +678,21 @@ namespace polysat {
     */
     template<typename Ext>
     bool fixplex<Ext>::propagate() {
-        lbool r;
-        while (!m_ineqs_to_propagate.empty()) {
-            unsigned idx = *m_ineqs_to_propagate.begin();        
-            if (idx < m_ineqs.size() && (r = propagate_ineqs(idx), r == l_false))
-                return false;
+        return propagate_ineqs() && propagate_row_bounds() && propagate_row_eqs();
+    }
+
+    template<typename Ext>
+    bool fixplex<Ext>::propagate_ineqs() {
+        lbool r = l_true;
+        while (!m_ineqs_to_propagate.empty() && r == l_true) {
+            unsigned idx = *m_ineqs_to_propagate.begin();  
+            if (idx >= m_ineqs.size()) {
+                m_ineqs_to_propagate.remove(idx);
+                continue;
+            }
+            r = propagate_ineqs(idx);
+            if (r == l_undef)
+                return true;
             m_ineqs_to_propagate.remove(idx);
         }        
         return true;
@@ -845,6 +862,9 @@ namespace polysat {
      * c           - coefficient of y in r_z
      * 
      * returns true if elimination preserves equivalence (is lossless).
+     * 
+     * TBD: add r_z.id() to m_eq_rows, m_bound_rows with some frequency?
+     * 
      */
     template<typename Ext>
     bool fixplex<Ext>::eliminate_var(
@@ -871,6 +891,7 @@ namespace polysat {
         return tz_b <= tz_c;
     }
 
+#if 0
     template<typename Ext>
     bool fixplex<Ext>::is_feasible() const {
         for (unsigned i = m_vars.size(); i-- > 0; )
@@ -878,6 +899,7 @@ namespace polysat {
                 return false;
         return true;
     }
+#endif
 
     /***
     * Record an infeasible row.
@@ -1055,9 +1077,11 @@ namespace polysat {
      */
 
     template<typename Ext>
-    void fixplex<Ext>::propagate_eqs() {
-        for (unsigned i = 0; i < m_rows.size(); ++i) 
-            get_offset_eqs(row(i));        
+    bool fixplex<Ext>::propagate_row_eqs() {
+        for (unsigned i : m_eq_rows)
+            get_offset_eqs(row(i));  
+        m_eq_rows.reset();
+        return !inconsistent();
     }
 
 
@@ -1113,11 +1137,10 @@ namespace polysat {
                 std::swap(z, u);
                 std::swap(cz, cu);
             }
-            if (z == x && u != y && cx == cz && cu == cy && value(u) == value(y)) 
+            if (z == x && find(u) != find(y) && cx == cz && cu == cy && value(u) == value(y)) 
                 eq_eh(u, y, m_deps.mk_join(row2dep(r1), row2dep(r2)));                
-            if (z == x && u != y && cx + cz == 0 && cu + cy == 0 && value(u) == value(y)) 
+            if (z == x && find(u) != find(y) && cx + cz == 0 && cu + cy == 0 && value(u) == value(y)) 
                 eq_eh(u, y, m_deps.mk_join(row2dep(r1), row2dep(r2)));
-
         }
     }
 
@@ -1129,8 +1152,8 @@ namespace polysat {
         numeral val = value(x);
         fix_entry e;
         if (m_value2fixed_var.find(val, e)) {
-            SASSERT(x != e.x);
-            eq_eh(x, e.x, m_deps.mk_join(e.dep, dep));
+            if (find(x) != find(e.x))
+                eq_eh(x, e.x, m_deps.mk_join(e.dep, dep));
         }
         else {
             m_value2fixed_var.insert(val, fix_entry(x, dep));
@@ -1141,23 +1164,20 @@ namespace polysat {
 
     template<typename Ext>
     void fixplex<Ext>::eq_eh(var_t x, var_t y, u_dependency* dep) {
+        SASSERT(find(x) != find(y));
+        merge(x, y);
         m_var_eqs.push_back(var_eq(x, y, dep));
         m_trail.push_back(trail_i::add_eq_i);
-    }    
+    }   
 
-#if 0
     template<typename Ext>
-    lbool fixplex<Ext>::propagate_bounds() {
-        lbool r = l_true;
-        for (unsigned i = 0; i < m_rows.size(); ++i) 
+    bool fixplex<Ext>::propagate_row_bounds() {
+        for (unsigned i : m_bound_rows)
             if (!propagate_row(row(i)))
-                return l_false;
-        for (auto ineq : m_ineqs) 
-            if (r = propagate_ineqs(ineq), r != l_true)
-                return r;
-        return l_true;
+                return false;
+        m_bound_rows.reset();
+        return true;
     }
-#endif
 
     //
     // DFS search propagating inequalities
diff --git a/src/test/fixplex.cpp b/src/test/fixplex.cpp
index 79048553b..e28cec4b8 100644
--- a/src/test/fixplex.cpp
+++ b/src/test/fixplex.cpp
@@ -114,7 +114,6 @@ namespace polysat {
         fp.add_row(z, 3, ys2, coeffs2);
         fp.set_bounds(u, 1, 2, 1);
         fp.run();
-        fp.propagate_eqs();
         for (auto e : fp.var_eqs())
             std::cout << e.x << " == " << e.y << "\n";
         
diff --git a/src/util/union_find.h b/src/util/union_find.h
index c82d25857..7e42e1bba 100644
--- a/src/util/union_find.h
+++ b/src/util/union_find.h
@@ -93,6 +93,11 @@ public:
         return r;
     }
 
+    void reserve(unsigned v) {
+        while (get_num_vars() <= v)
+            mk_var();
+    }
+
     unsigned get_num_vars() const { return m_find.size(); }