diff --git a/scripts/mk_project.py b/scripts/mk_project.py
index 88a7e6414..6fb377a80 100644
--- a/scripts/mk_project.py
+++ b/scripts/mk_project.py
@@ -49,7 +49,7 @@ def init_project_def():
     add_lib('core_tactics', ['tactic', 'macros', 'normal_forms', 'rewriter', 'pattern'], 'tactic/core')
     add_lib('arith_tactics', ['core_tactics', 'sat'], 'tactic/arith')
 
-    add_lib('sat_smt', ['sat', 'euf', 'tactic', 'smt_params', 'bit_blaster'], 'sat/smt')
+    add_lib('sat_smt', ['sat', 'euf', 'tactic', 'solver', 'smt_params', 'bit_blaster'], 'sat/smt')
     add_lib('sat_tactic', ['tactic', 'sat', 'solver', 'sat_smt'], 'sat/tactic')
     add_lib('nlsat_tactic', ['nlsat', 'sat_tactic', 'arith_tactics'], 'nlsat/tactic')
     add_lib('subpaving_tactic', ['core_tactics', 'subpaving'], 'math/subpaving/tactic')
diff --git a/src/api/api_solver.cpp b/src/api/api_solver.cpp
index 5c711019f..049ed9f59 100644
--- a/src/api/api_solver.cpp
+++ b/src/api/api_solver.cpp
@@ -974,7 +974,7 @@ extern "C" {
         Z3_TRY;
         LOG_Z3_solver_propagate_consequence(c, s, num_fixed, fixed_ids, num_eqs, eq_lhs, eq_rhs, conseq);
         RESET_ERROR_CODE();
-        reinterpret_cast<solver::propagate_callback*>(s)->propagate(num_fixed, fixed_ids, num_eqs, eq_lhs, eq_rhs, to_expr(conseq));
+        reinterpret_cast<solver::propagate_callback*>(s)->propagate_cb(num_fixed, fixed_ids, num_eqs, eq_lhs, eq_rhs, to_expr(conseq));
         Z3_CATCH;        
     }
 
diff --git a/src/math/lp/lar_solver.h b/src/math/lp/lar_solver.h
index df0c9a1b6..e36483d8c 100644
--- a/src/math/lp/lar_solver.h
+++ b/src/math/lp/lar_solver.h
@@ -134,9 +134,6 @@ class lar_solver : public column_namer {
     void add_row_from_term_no_constraint(const lar_term * term, unsigned term_ext_index);
     void add_basic_var_to_core_fields();
     bool compare_values(impq const& lhs, lconstraint_kind k, const mpq & rhs);
-    // columns
-    bool column_is_int(column_index const& j) const { return column_is_int((unsigned)j); }
-    const impq& get_value(column_index const& j) const { return get_column_value(j); }
 
 
     void update_column_type_and_bound_check_on_equal(unsigned j, lconstraint_kind kind, const mpq & right_side, constraint_index constr_index, unsigned&);
@@ -626,6 +623,9 @@ public:
     inline bool column_value_is_int(unsigned j) const { return m_mpq_lar_core_solver.m_r_x[j].is_int(); }
     inline static_matrix<mpq, impq> & A_r() { return m_mpq_lar_core_solver.m_r_A; }
     inline const static_matrix<mpq, impq> & A_r() const { return m_mpq_lar_core_solver.m_r_A; }
+    // columns
+    bool column_is_int(column_index const& j) const { return column_is_int((unsigned)j); }
+    const impq& get_value(column_index const& j) const { return get_column_value(j); }
     const impq& get_column_value(unsigned j) const { return m_mpq_lar_core_solver.m_r_x[j]; }
     inline
     var_index external_to_local(unsigned j) const {
diff --git a/src/sat/sat_extension.h b/src/sat/sat_extension.h
index 71214055d..8b5ef3fe3 100644
--- a/src/sat/sat_extension.h
+++ b/src/sat/sat_extension.h
@@ -57,11 +57,15 @@ namespace sat {
     protected:
         bool m_drating { false };
         int  m_id { 0 };
+        solver* m_solver { nullptr };
     public:        
         extension(int id): m_id(id) {}
         virtual ~extension() {}
-        virtual int get_id() const { return m_id; }
-        virtual void set_solver(solver* s) = 0;
+        int get_id() const { return m_id; }
+        void set_solver(solver* s) { m_solver = s; }        
+        solver& s() { return *m_solver; }
+        solver const& s() const { return *m_solver; }
+
         virtual void set_lookahead(lookahead* s) {};
         class scoped_drating {
             extension& ext;
@@ -70,13 +74,13 @@ namespace sat {
             ~scoped_drating() { ext.m_drating = false;  }
         };
         virtual void init_search() {}
-        virtual bool propagate(literal l, ext_constraint_idx idx) = 0;
-        virtual bool unit_propagate() = 0;
-        virtual bool is_external(bool_var v) = 0;
+        virtual bool propagate(sat::literal l, sat::ext_constraint_idx idx) { UNREACHABLE(); return false; }
+        virtual bool unit_propagate() = 0;        
+        virtual bool is_external(bool_var v) { return false; }
         virtual double get_reward(literal l, ext_constraint_idx idx, literal_occs_fun& occs) const { return 0; }
         virtual void get_antecedents(literal l, ext_justification_idx idx, literal_vector & r, bool probing) = 0;
         virtual bool is_extended_binary(ext_justification_idx idx, literal_vector & r) { return false; }
-        virtual void asserted(literal l) = 0;
+        virtual void asserted(literal l) {};
         virtual check_result check() = 0;
         virtual lbool resolve_conflict() { return l_undef; } // stores result in sat::solver::m_lemma
         virtual void push() = 0;
diff --git a/src/sat/sat_solver/inc_sat_solver.cpp b/src/sat/sat_solver/inc_sat_solver.cpp
index a7dda80a4..e507c9a5f 100644
--- a/src/sat/sat_solver/inc_sat_solver.cpp
+++ b/src/sat/sat_solver/inc_sat_solver.cpp
@@ -624,6 +624,39 @@ public:
         m_preprocess->reset();
     }
 
+    euf::solver* ensure_euf() {
+        auto* ext = dynamic_cast<euf::solver*>(m_solver.get_extension());
+        return ext;
+    }
+
+    void user_propagate_init(
+        void*                ctx, 
+        solver::push_eh_t&   push_eh,
+        solver::pop_eh_t&    pop_eh,
+        solver::fresh_eh_t&  fresh_eh) override {
+        ensure_euf()->user_propagate_init(ctx, push_eh, pop_eh, fresh_eh);
+    }
+        
+    void user_propagate_register_fixed(solver::fixed_eh_t& fixed_eh) override {
+        ensure_euf()->user_propagate_register_fixed(fixed_eh);
+    }
+    
+    void user_propagate_register_final(solver::final_eh_t& final_eh) override {
+        ensure_euf()->user_propagate_register_final(final_eh);
+    }
+    
+    void user_propagate_register_eq(solver::eq_eh_t& eq_eh) override {
+        ensure_euf()->user_propagate_register_eq(eq_eh);
+    }
+    
+    void user_propagate_register_diseq(solver::eq_eh_t& diseq_eh) override {
+        ensure_euf()->user_propagate_register_diseq(diseq_eh);
+    }
+    
+    unsigned user_propagate_register(expr* e) override { 
+        return ensure_euf()->user_propagate_register(e);
+    }
+
 private:
 
     lbool internalize_goal(goal_ref& g) {        
diff --git a/src/sat/smt/CMakeLists.txt b/src/sat/smt/CMakeLists.txt
index 7f1f54059..5556333fc 100644
--- a/src/sat/smt/CMakeLists.txt
+++ b/src/sat/smt/CMakeLists.txt
@@ -25,6 +25,7 @@ z3_add_component(sat_smt
     euf_solver.cpp
     sat_dual_solver.cpp
     sat_th.cpp
+    user_solver.cpp
     xor_solver.cpp
   COMPONENT_DEPENDENCIES
     sat
diff --git a/src/sat/smt/array_solver.h b/src/sat/smt/array_solver.h
index d7bd88d9d..afff61219 100644
--- a/src/sat/smt/array_solver.h
+++ b/src/sat/smt/array_solver.h
@@ -60,14 +60,12 @@ namespace array {
 
         array_util        a;
         stats             m_stats;
-        sat::solver*      m_solver{ nullptr };
         scoped_ptr_vector<var_data>          m_var_data;
         ast2ast_trailmap<sort, app>          m_sort2epsilon;
         ast2ast_trailmap<sort, func_decl>    m_sort2diag;
         obj_map<sort, func_decl_ref_vector*> m_sort2diff;
         array_union_find                     m_find;
 
-        sat::solver& s() { return *m_solver; }
         theory_var find(theory_var v) { return m_find.find(v); }
 
         // internalize
@@ -187,7 +185,6 @@ namespace array {
     public:
         solver(euf::solver& ctx, theory_id id);
         ~solver() override {}
-        void set_solver(sat::solver* s) override { m_solver = s; }
         bool is_external(bool_var v) override { return false; }
         bool propagate(literal l, sat::ext_constraint_idx idx) override { UNREACHABLE(); return false; }
         void get_antecedents(literal l, sat::ext_justification_idx idx, literal_vector& r, bool probing) override {}
diff --git a/src/sat/smt/ba_solver.cpp b/src/sat/smt/ba_solver.cpp
index d27726f5f..2155a7c39 100644
--- a/src/sat/smt/ba_solver.cpp
+++ b/src/sat/smt/ba_solver.cpp
@@ -1365,7 +1365,7 @@ namespace sat {
     ba_solver::ba_solver(ast_manager& m, sat::sat_internalizer& si, euf::theory_id id)
         : euf::th_solver(m, id),
           si(si), m_pb(m),
-          m_solver(nullptr), m_lookahead(nullptr), 
+          m_lookahead(nullptr), 
           m_constraint_id(0), m_ba(*this), m_sort(m_ba) {
         TRACE("ba", tout << this << "\n";);
         m_num_propagations_since_pop = 0;
@@ -3579,14 +3579,14 @@ namespace sat {
         switch (cnstr.tag()) {
         case ba::tag_t::card_t: {
             card& c = cnstr.to_card();
-            ineq.reset(offset*c.k());
+            ineq.reset(static_cast<uint64_t>(offset)*c.k());
             for (literal l : c) ineq.push(l, offset);
             if (c.lit() != null_literal) ineq.push(~c.lit(), offset*c.k());                
             break;
         }
         case ba::tag_t::pb_t: {
             pb& p = cnstr.to_pb();
-            ineq.reset(offset * p.k());
+            ineq.reset(static_cast<uint64_t>(offset) * p.k());
             for (wliteral wl : p) ineq.push(wl.second, offset * wl.first);
             if (p.lit() != null_literal) ineq.push(~p.lit(), offset * p.k());
             break;
diff --git a/src/sat/smt/ba_solver.h b/src/sat/smt/ba_solver.h
index 855b16410..81132ecec 100644
--- a/src/sat/smt/ba_solver.h
+++ b/src/sat/smt/ba_solver.h
@@ -86,7 +86,6 @@ namespace sat {
         sat_internalizer&      si;
         pb_util                m_pb;
 
-        solver*                m_solver{ nullptr };
         lookahead*             m_lookahead{ nullptr };
         stats                  m_stats; 
         small_object_allocator m_allocator;
@@ -140,9 +139,6 @@ namespace sat {
         void     inc_parity(bool_var v);
         void     reset_parity(bool_var v);
 
-        solver& s() const { return *m_solver; }
-
-
         // simplification routines
 
         vector<svector<constraint*>>    m_cnstr_use_list;
@@ -400,7 +396,6 @@ namespace sat {
         ba_solver(euf::solver& ctx, euf::theory_id id);
         ba_solver(ast_manager& m, sat::sat_internalizer& si, euf::theory_id id);
         ~ba_solver() override;
-        void set_solver(solver* s) override { m_solver = s; }
         void set_lookahead(lookahead* l) override { m_lookahead = l; }
         void add_at_least(bool_var v, literal_vector const& lits, unsigned k);
         void add_pb_ge(bool_var v, svector<wliteral> const& wlits, unsigned k);
diff --git a/src/sat/smt/bv_solver.cpp b/src/sat/smt/bv_solver.cpp
index bd82410bc..e292e52f3 100644
--- a/src/sat/smt/bv_solver.cpp
+++ b/src/sat/smt/bv_solver.cpp
@@ -62,9 +62,14 @@ namespace bv {
     void solver::fixed_var_eh(theory_var v1) {
         numeral val1, val2;
         VERIFY(get_fixed_value(v1, val1));
+        euf::enode* n1 = var2enode(v1);
         unsigned sz = m_bits[v1].size();
         value_sort_pair key(val1, sz);
         theory_var v2;
+        if (ctx.watches_fixed(n1)) {
+            expr_ref value(bv.mk_numeral(val1, sz), m);
+            ctx.assign_fixed(n1, value, m_bits[v1]);
+        }
         bool is_current =
             m_fixed_var_table.find(key, v2) &&
             v2 < static_cast<int>(get_num_vars()) &&
@@ -74,12 +79,12 @@ namespace bv {
 
         if (!is_current)
             m_fixed_var_table.insert(key, v1);
-        else if (var2enode(v1)->get_root() != var2enode(v2)->get_root()) {
+        else if (n1->get_root() != var2enode(v2)->get_root()) {
             SASSERT(get_bv_size(v1) == get_bv_size(v2));
             TRACE("bv", tout << "detected equality: v" << v1 << " = v" << v2 << "\n" << pp(v1) << pp(v2););
             m_stats.m_num_bit2eq++;
             add_fixed_eq(v1, v2);
-            ctx.propagate(var2enode(v1), var2enode(v2), mk_bit2eq_justification(v1, v2));
+            ctx.propagate(n1, var2enode(v2), mk_bit2eq_justification(v1, v2));
         }
     }
 
diff --git a/src/sat/smt/bv_solver.h b/src/sat/smt/bv_solver.h
index e29ecffdf..82c72ca1d 100644
--- a/src/sat/smt/bv_solver.h
+++ b/src/sat/smt/bv_solver.h
@@ -233,11 +233,6 @@ namespace bv {
         unsigned_vector            m_prop_queue_lim;
         unsigned                   m_prop_queue_head { 0 };
 
-
-        sat::solver* m_solver;
-        sat::solver& s() { return *m_solver;  }
-        sat::solver const& s() const { return *m_solver;  }
-
         // internalize
         void insert_bv2a(bool_var bv, atom * a) { m_bool_var2atom.setx(bv, a, 0); }
         void erase_bv2a(bool_var bv) { m_bool_var2atom[bv] = 0; }
@@ -327,7 +322,6 @@ namespace bv {
     public:
         solver(euf::solver& ctx, theory_id id);
         ~solver() override {}
-        void set_solver(sat::solver* s) override { m_solver = s; }
         void set_lookahead(sat::lookahead* s) override { }
         void init_search() override {}
         double get_reward(literal l, sat::ext_constraint_idx idx, sat::literal_occs_fun& occs) const override;
diff --git a/src/sat/smt/euf_solver.cpp b/src/sat/smt/euf_solver.cpp
index f80a1d25a..d7c08a14d 100644
--- a/src/sat/smt/euf_solver.cpp
+++ b/src/sat/smt/euf_solver.cpp
@@ -33,7 +33,6 @@ namespace euf {
         m_trail(*this),
         m_rewriter(m),
         m_unhandled_functions(m),
-        m_solver(nullptr),
         m_lookahead(nullptr),
         m_to_m(&m),
         m_to_si(&si),
@@ -670,4 +669,27 @@ namespace euf {
         return true;
     }
 
+    void solver::user_propagate_init(
+        void* ctx,
+        ::solver::push_eh_t& push_eh,
+        ::solver::pop_eh_t& pop_eh,
+        ::solver::fresh_eh_t& fresh_eh) {
+        m_user_propagator = alloc(user::solver, *this);
+        m_user_propagator->add(ctx, push_eh, pop_eh, fresh_eh);
+        for (unsigned i = m_scopes.size(); i-- > 0; )
+            m_user_propagator->push();
+        m_solvers.push_back(m_user_propagator);
+        m_id2solver.setx(m_user_propagator->get_id(), m_user_propagator, nullptr);
+    }
+
+    bool solver::watches_fixed(enode* n) const {
+        return m_user_propagator && m_user_propagator->has_fixed() && n->get_th_var(m_user_propagator->get_id()) != null_theory_var;
+    }
+
+    void solver::assign_fixed(enode* n, expr* val, unsigned sz, literal const* explain) {
+        theory_var v = n->get_th_var(m_user_propagator->get_id());
+        m_user_propagator->new_fixed_eh(v, val, sz, explain);
+    }
+
+
 }
diff --git a/src/sat/smt/euf_solver.h b/src/sat/smt/euf_solver.h
index 3fc3b6d56..ace5b383e 100644
--- a/src/sat/smt/euf_solver.h
+++ b/src/sat/smt/euf_solver.h
@@ -27,6 +27,7 @@ Author:
 #include "sat/smt/sat_th.h"
 #include "sat/smt/sat_dual_solver.h"
 #include "sat/smt/euf_ackerman.h"
+#include "sat/smt/user_solver.h"
 #include "smt/params/smt_params.h"
 
 namespace euf {
@@ -85,13 +86,12 @@ namespace euf {
         stats                 m_stats;
         th_rewriter           m_rewriter;
         func_decl_ref_vector  m_unhandled_functions;
-
-        sat::solver* m_solver{ nullptr };
-        sat::lookahead* m_lookahead{ nullptr };
-        ast_manager* m_to_m;
+        sat::lookahead*       m_lookahead{ nullptr };
+        ast_manager*           m_to_m;
         sat::sat_internalizer* m_to_si;
         scoped_ptr<euf::ackerman>   m_ackerman;
         scoped_ptr<sat::dual_solver> m_dual_solver;
+        user::solver*          m_user_propagator{ nullptr };
 
         ptr_vector<expr>                                m_var2expr;
         ptr_vector<size_t>                              m_explain;
@@ -174,6 +174,12 @@ namespace euf {
         constraint& eq_constraint() { return mk_constraint(m_eq, constraint::kind_t::eq); }
         constraint& lit_constraint() { return mk_constraint(m_lit, constraint::kind_t::lit); }
 
+        // user propagator
+        void check_for_user_propagator() {
+            if (!m_user_propagator)
+                throw default_exception("user propagator must be initialized");
+        }
+
     public:
         solver(ast_manager& m, sat::sat_internalizer& si, params_ref const& p = params_ref());
 
@@ -197,8 +203,7 @@ namespace euf {
         };
 
         // accessors
-        sat::solver& s() { return *m_solver; }
-        sat::solver const& s() const { return *m_solver; }
+        
         sat::sat_internalizer& get_si() { return si; }
         ast_manager& get_manager() { return m; }
         enode* get_enode(expr* e) { return m_egraph.find(e); }
@@ -212,7 +217,6 @@ namespace euf {
         euf_trail_stack& get_trail_stack() { return m_trail; }
 
         void updt_params(params_ref const& p);
-        void set_solver(sat::solver* s) override { m_solver = s; }
         void set_lookahead(sat::lookahead* s) override { m_lookahead = s; }
         void init_search() override;
         double get_reward(literal l, ext_constraint_idx idx, sat::literal_occs_fun& occs) const override;
@@ -285,6 +289,40 @@ namespace euf {
 
         // diagnostics
         func_decl_ref_vector const& unhandled_functions() { return m_unhandled_functions; }
+
+        // user propagator
+        void user_propagate_init(
+            void* ctx,
+            ::solver::push_eh_t& push_eh,
+            ::solver::pop_eh_t& pop_eh,
+            ::solver::fresh_eh_t& fresh_eh);
+        bool watches_fixed(enode* n) const;
+        void assign_fixed(enode* n, expr* val, unsigned sz, literal const* explain);
+        void assign_fixed(enode* n, expr* val, literal_vector const& explain) { assign_fixed(n, val, explain.size(), explain.c_ptr()); }
+        void assign_fixed(enode* n, expr* val, literal explain) { assign_fixed(n, val, 1, &explain); }
+
+        void user_propagate_register_final(::solver::final_eh_t& final_eh) {
+            check_for_user_propagator();
+            m_user_propagator->register_final(final_eh);
+        }
+        void user_propagate_register_fixed(::solver::fixed_eh_t& fixed_eh) {
+            check_for_user_propagator();
+            m_user_propagator->register_fixed(fixed_eh);
+        }
+        void user_propagate_register_eq(::solver::eq_eh_t& eq_eh) {
+            check_for_user_propagator();
+            m_user_propagator->register_eq(eq_eh);
+        }
+        void user_propagate_register_diseq(::solver::eq_eh_t& diseq_eh) {
+            check_for_user_propagator();
+            m_user_propagator->register_diseq(diseq_eh);
+        }
+        unsigned user_propagate_register(expr* e) {
+            check_for_user_propagator();
+            return m_user_propagator->add_expr(e);
+        }
+
+
     };
 };
 
diff --git a/src/sat/smt/user_solver.cpp b/src/sat/smt/user_solver.cpp
new file mode 100644
index 000000000..e12e57a6d
--- /dev/null
+++ b/src/sat/smt/user_solver.cpp
@@ -0,0 +1,159 @@
+/*++
+Copyright (c) 2020 Microsoft Corporation
+
+Module Name:
+
+    user_solver.cpp
+
+Abstract:
+
+    User propagator plugin.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2020-09-23
+
+--*/
+
+#include "sat/smt/user_solver.h"
+#include "sat/smt/euf_solver.h"
+
+namespace user {
+
+    solver::solver(euf::solver& ctx) :
+        th_euf_solver(ctx, ctx.get_manager().mk_family_id("user"))
+    {}
+
+    solver::~solver() {
+        dealloc(m_api_context);
+    }
+
+    unsigned solver::add_expr(expr* e) {
+        force_push();
+        ctx.internalize(e, false);
+        euf::enode* n = expr2enode(e);
+        if (is_attached_to_var(n))
+            return n->get_th_var(get_id());
+        euf::theory_var v = mk_var(n);
+        ctx.attach_th_var(n, this, v);
+        return v;
+    }
+
+    void solver::propagate_cb(
+        unsigned num_fixed, unsigned const* fixed_ids,
+        unsigned num_eqs, unsigned const* eq_lhs, unsigned const* eq_rhs,
+        expr* conseq) {
+        m_prop.push_back(prop_info(num_fixed, fixed_ids, num_eqs, eq_lhs, eq_rhs, expr_ref(conseq, m)));
+    }
+
+    sat::check_result solver::check() {
+        if (!(bool)m_final_eh)
+            return  sat::check_result::CR_DONE;
+        unsigned sz = m_prop.size();
+        m_final_eh(m_user_context, this);
+        return sz == m_prop.size() ? sat::check_result::CR_DONE : sat::check_result::CR_CONTINUE;
+    }
+
+    void solver::new_fixed_eh(euf::theory_var v, expr* value, unsigned num_lits, sat::literal const* jlits) {
+        if (!m_fixed_eh)
+            return;
+        force_push();
+        m_id2justification.setx(v, sat::literal_vector(num_lits, jlits), sat::literal_vector());
+        m_fixed_eh(m_user_context, this, v, value);
+    }
+
+    void solver::asserted(sat::literal lit) {
+        if (!m_fixed_eh)
+            return;
+        force_push();
+        auto* n = bool_var2enode(lit.var());
+        euf::theory_var v = n->get_th_var(get_id());
+        sat::literal_vector lits;
+        lits.push_back(lit);
+        m_id2justification.setx(v, lits, sat::literal_vector());
+        m_fixed_eh(m_user_context, this, v, lit.sign() ? m.mk_false() : m.mk_true());
+    }
+
+    void solver::push_core() {
+        th_euf_solver::push_core();
+        m_prop_lim.push_back(m_prop.size());
+        m_push_eh(m_user_context);
+    }
+
+    void solver::pop_core(unsigned num_scopes) {
+        th_euf_solver::pop_core(num_scopes);
+        unsigned old_sz = m_prop_lim.size() - num_scopes;
+        m_prop.shrink(m_prop_lim[old_sz]);
+        m_prop_lim.shrink(old_sz);
+        m_pop_eh(m_user_context, num_scopes);
+    }
+
+    bool solver::unit_propagate() {
+        if (m_qhead == m_prop.size())
+            return false;
+        force_push();
+        ctx.push(value_trail<euf::solver, unsigned>(m_qhead));
+        unsigned np = m_stats.m_num_propagations;
+        for (; m_qhead < m_prop.size() && !s().inconsistent(); ++m_qhead) {
+            auto const& prop = m_prop[m_qhead];
+            sat::literal lit = ctx.internalize(prop.m_conseq, false, false, true);
+            if (s().value(lit) != l_true) {
+                s().assign(lit, mk_justification(m_qhead));
+                ++m_stats.m_num_propagations;
+            }
+        }       
+        return np < m_stats.m_num_propagations;
+    }
+
+    void solver::collect_statistics(::statistics& st) const {
+        st.update("user-propagations", m_stats.m_num_propagations);
+        st.update("user-watched", get_num_vars());
+    }
+
+    sat::justification solver::mk_justification(unsigned prop_idx) {
+        void* mem = get_region().allocate(justification::get_obj_size());
+        sat::constraint_base::initialize(mem, this);
+        auto* constraint = new (sat::constraint_base::ptr2mem(mem)) justification(prop_idx);
+        return sat::justification::mk_ext_justification(s().scope_lvl(), constraint->to_index());
+    }
+
+    void solver::get_antecedents(sat::literal l, sat::ext_justification_idx idx, sat::literal_vector & r, bool probing) {
+        auto& j = justification::from_index(idx);
+        auto const& prop = m_prop[j.m_propagation_index];
+        for (unsigned id : prop.m_ids)
+            r.append(m_id2justification[id]);
+        for (auto const& p : prop.m_eqs)
+            ctx.add_antecedent(var2enode(p.first), var2enode(p.second));
+    }
+
+    std::ostream& solver::display(std::ostream& out) const {
+        for (unsigned i = 0; i < get_num_vars(); ++i)
+            out << i << ": " << mk_pp(var2expr(i), m) << "\n";
+        return out;
+    }
+
+    std::ostream& solver::display_justification(std::ostream& out, sat::ext_justification_idx idx) const {
+        auto& j = justification::from_index(idx);
+        auto const& prop = m_prop[j.m_propagation_index];
+        for (unsigned id : prop.m_ids)
+            out << id << ": " << m_id2justification[id];
+        for (auto const& p : prop.m_eqs)
+            out << "v" << p.first << " == v" << p.second << " ";
+        return out;
+    }
+
+    std::ostream& solver::display_constraint(std::ostream& out, sat::ext_constraint_idx idx) const {
+        return display_justification(out, idx);     
+    }
+
+    euf::th_solver* solver::fresh(sat::solver* dst_s, euf::solver& dst_ctx) {
+        auto* result = alloc(solver, dst_ctx);
+        result->set_solver(dst_s);
+        ast_translation tr(m, dst_ctx.get_manager(), false);
+        for (unsigned i = 0; i < get_num_vars(); ++i) 
+            result->add_expr(tr(var2expr(i)));
+        return result;
+    }
+
+}
+
diff --git a/src/sat/smt/user_solver.h b/src/sat/smt/user_solver.h
new file mode 100644
index 000000000..c7df05ad0
--- /dev/null
+++ b/src/sat/smt/user_solver.h
@@ -0,0 +1,130 @@
+/*++
+Copyright (c) 2020 Microsoft Corporation
+
+Module Name:
+
+    user_solver.h
+
+Abstract:
+
+    User-propagator plugin.
+    Adds user plugins to propagate based on 
+    terms receiving fixed values or equalities.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2020-08-17
+
+--*/
+
+#pragma once
+
+#include "sat/smt/sat_th.h"
+#include "solver/solver.h"
+
+
+namespace user {
+
+    class solver : public euf::th_euf_solver, public ::solver::propagate_callback {
+
+        struct prop_info {
+            unsigned_vector m_ids;
+            expr_ref        m_conseq;
+            svector<std::pair<unsigned, unsigned>> m_eqs;
+            prop_info(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* eq_lhs, unsigned const* eq_rhs, expr_ref const& c):
+                m_ids(num_fixed, fixed_ids),
+                m_conseq(c)
+            {
+                for (unsigned i = 0; i < num_eqs; ++i)
+                    m_eqs.push_back(std::make_pair(eq_lhs[i], eq_rhs[i]));
+            }
+        };
+
+        struct stats {
+            unsigned m_num_propagations;
+            stats() { reset(); }
+            void reset() { memset(this, 0, sizeof(*this)); }
+        };
+
+        void*                  m_user_context;
+        ::solver::push_eh_t      m_push_eh;
+        ::solver::pop_eh_t       m_pop_eh;
+        ::solver::fresh_eh_t     m_fresh_eh;
+        ::solver::final_eh_t     m_final_eh;
+        ::solver::fixed_eh_t     m_fixed_eh;
+        ::solver::eq_eh_t        m_eq_eh;
+        ::solver::eq_eh_t        m_diseq_eh;
+        ::solver::context_obj*   m_api_context { nullptr };
+        unsigned               m_qhead { 0 };
+        vector<prop_info>      m_prop;
+        unsigned_vector        m_prop_lim;
+        vector<sat::literal_vector> m_id2justification;
+        unsigned               m_num_scopes { 0 };
+        sat::literal_vector         m_lits;
+        euf::enode_pair_vector      m_eqs;
+        stats                  m_stats;
+
+        struct justification {
+            unsigned m_propagation_index { 0 };
+
+            justification(unsigned prop_index): m_propagation_index(prop_index) {}
+
+            sat::ext_constraint_idx to_index() const { 
+                return sat::constraint_base::mem2base(this); 
+            }
+            static justification& from_index(size_t idx) {
+                return *reinterpret_cast<justification*>(sat::constraint_base::from_index(idx)->mem());
+            }
+            static size_t get_obj_size() { return sat::constraint_base::obj_size(sizeof(justification)); }
+        };
+
+        sat::justification mk_justification(unsigned propagation_index);
+
+    public:
+        solver(euf::solver& ctx);
+        
+        ~solver() override;
+
+        /*
+         * \brief initial setup for user propagator.
+         */
+        void add(
+            void*                 ctx, 
+            ::solver::push_eh_t&    push_eh,
+            ::solver::pop_eh_t&     pop_eh,
+            ::solver::fresh_eh_t&   fresh_eh) {
+            m_user_context = ctx;
+            m_push_eh      = push_eh;
+            m_pop_eh       = pop_eh;
+            m_fresh_eh     = fresh_eh;
+        }
+
+        unsigned add_expr(expr* e);
+
+        void register_final(::solver::final_eh_t& final_eh) { m_final_eh = final_eh; }
+        void register_fixed(::solver::fixed_eh_t& fixed_eh) { m_fixed_eh = fixed_eh; }
+        void register_eq(::solver::eq_eh_t& eq_eh) { m_eq_eh = eq_eh; }
+        void register_diseq(::solver::eq_eh_t& diseq_eh) { m_diseq_eh = diseq_eh; }
+
+        bool has_fixed() const { return (bool)m_fixed_eh; }
+
+        void propagate_cb(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* lhs, unsigned const* rhs, expr* conseq) override;
+
+        void new_fixed_eh(euf::theory_var v, expr* value, unsigned num_lits, sat::literal const* jlits);
+
+        void asserted(sat::literal lit) override;
+        sat::check_result check() override;
+        void push_core() override;
+        void pop_core(unsigned n) override;
+        bool unit_propagate() override;
+        void get_antecedents(sat::literal l, sat::ext_justification_idx idx, sat::literal_vector & r, bool probing) override;
+        void collect_statistics(statistics& st) const override;
+        sat::literal internalize(expr* e, bool sign, bool root, bool learned) override { UNREACHABLE(); return sat::null_literal; }
+        void internalize(expr* e, bool redundant) override { UNREACHABLE(); }
+        std::ostream& display(std::ostream& out) const override;
+        std::ostream& display_justification(std::ostream& out, sat::ext_justification_idx idx) const override;
+        std::ostream& display_constraint(std::ostream& out, sat::ext_constraint_idx idx) const override;
+        euf::th_solver* fresh(sat::solver* s, euf::solver& ctx) override;
+
+    };
+};
diff --git a/src/smt/theory_lra.cpp b/src/smt/theory_lra.cpp
index 16e4cd4f0..534964344 100644
--- a/src/smt/theory_lra.cpp
+++ b/src/smt/theory_lra.cpp
@@ -2385,6 +2385,7 @@ public:
         TRACE("arith", tout << "v" << v << " " << be.kind() << " " << be.m_bound << "\n";);
 
         ensure_bounds(v);
+
             
         if (m_unassigned_bounds[v] == 0 && !should_refine_bounds()) {
             TRACE("arith", tout << "return\n";);
diff --git a/src/smt/user_propagator.cpp b/src/smt/user_propagator.cpp
index 42450056e..22fa4e279 100644
--- a/src/smt/user_propagator.cpp
+++ b/src/smt/user_propagator.cpp
@@ -48,7 +48,7 @@ unsigned user_propagator::add_expr(expr* e) {
     return v;
 }
 
-void user_propagator::propagate(
+void user_propagator::propagate_cb(
     unsigned num_fixed, unsigned const* fixed_ids, 
     unsigned num_eqs, unsigned const* eq_lhs, unsigned const* eq_rhs, 
     expr* conseq) {
diff --git a/src/smt/user_propagator.h b/src/smt/user_propagator.h
index 9aa6d87d7..544a9ed0e 100644
--- a/src/smt/user_propagator.h
+++ b/src/smt/user_propagator.h
@@ -95,7 +95,7 @@ namespace smt {
 
         bool has_fixed() const { return (bool)m_fixed_eh; }
 
-        void propagate(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* lhs, unsigned const* rhs, expr* conseq) override;
+        void propagate_cb(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* lhs, unsigned const* rhs, expr* conseq) override;
 
         void new_fixed_eh(theory_var v, expr* value, unsigned num_lits, literal const* jlits);
 
diff --git a/src/solver/solver.h b/src/solver/solver.h
index a72620097..513572ab2 100644
--- a/src/solver/solver.h
+++ b/src/solver/solver.h
@@ -241,7 +241,7 @@ public:
 
     class propagate_callback {
     public:
-        virtual void propagate(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* eq_lhs, unsigned const* eq_rhs, expr* conseq) = 0;
+        virtual void propagate_cb(unsigned num_fixed, unsigned const* fixed_ids, unsigned num_eqs, unsigned const* eq_lhs, unsigned const* eq_rhs, expr* conseq) = 0;
     };
     class context_obj {
     public: