diff --git a/src/solver/CMakeLists.txt b/src/solver/CMakeLists.txt
index 67549c46b..1ed8fc674 100644
--- a/src/solver/CMakeLists.txt
+++ b/src/solver/CMakeLists.txt
@@ -6,6 +6,7 @@ z3_add_component(solver
     mus.cpp
     parallel_tactic.cpp
     smt_logics.cpp
+    smtmus.cpp
     solver.cpp
     solver_na2as.cpp
     solver_pool.cpp
diff --git a/src/solver/smtmus.cpp b/src/solver/smtmus.cpp
new file mode 100644
index 000000000..4784f2a01
--- /dev/null
+++ b/src/solver/smtmus.cpp
@@ -0,0 +1,127 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    musrmr.cpp
+
+Abstract:
+   
+    MUS extraction with model rotation modulo arithmatic.
+
+Author:
+
+    Jaroslav Bendik, Nikolaj Bjorner (nbjorner) 2021-12-20
+
+--*/
+
+#include "solver/solver.h"
+#include "solver/smtmus.h"
+#include "ast/ast_pp.h"
+#include "ast/ast_util.h"
+#include "model/model_evaluator.h"
+#include "ast/arith_decl_plugin.h"
+
+
+struct smtmus::imp {
+
+    typedef obj_hashtable<expr> expr_set;
+
+    solver&                  m_solver;
+    ast_manager&             m;
+    expr_ref_vector          m_lit2expr;
+    obj_map<expr, unsigned>  m_expr2lit;
+    model_ref                m_model;
+    expr_ref_vector          m_soft;
+    vector<expr_ref_vector>  m_soft_clauses;
+    obj_map<expr, expr_ref_vector*> m_lit2vars;
+
+    imp(solver& s): 
+        m_solver(s), m(s.get_manager()), m_lit2expr(m),  m_soft(m)
+    {}
+
+    ~imp() {
+        for (auto& [k, v] : m_lit2vars)
+            dealloc(v);
+    }
+
+    
+    unsigned add_soft(expr* lit) {
+        unsigned idx = m_lit2expr.size();
+        m_expr2lit.insert(lit, idx);
+        m_lit2expr.push_back(lit);
+        TRACE("mus", tout << idx << ": " << mk_pp(lit, m) << "\n" << m_lit2expr << "\n";);
+        return idx;
+    }
+
+    void init() {
+        // initialize soft_clauses based on control variables in mus, or if mus already is a clause.
+    }
+
+
+    lbool get_mus(expr_ref_vector& mus) {
+        m_model.reset();
+        mus.reset();
+        if (m_lit2expr.size() == 1) {
+            mus.push_back(m_lit2expr.back());
+            return l_true;
+        }
+        return l_undef;
+    }
+
+    // extract clauses corresponding to added soft constraints.
+    // extract integer, real variables from clauses
+    //
+
+    unsigned rotate(bool_vector& crits, unsigned i, model& mdl, bool top_level) {
+        unsigned rot = 0;
+        for (auto const& lit : m_soft_clauses[i]) {
+            auto const& vars = get_vars(lit);
+            for (expr* v : vars) {
+                expr_ref_vector flips = rotate_get_flips(lit, v, mdl, 1);
+                for (auto& flip : flips) {
+                    NOT_IMPLEMENTED_YET();
+                }
+            }
+        }
+    }
+
+    // access and update lit2vars on demand.
+    expr_ref_vector const& get_vars(expr* lit) {
+        if (!m_lit2vars.contains(lit)) {
+            expr_ref_vector* vars = alloc(expr_ref_vector, m);
+            extract_vars(lit, *vars);
+            m_lit2vars.insert(lit, vars);            
+        }
+        return *m_lit2vars[lit];
+    }
+
+    void extract_vars(expr* e, expr_ref_vector& vars) {
+        NOT_IMPLEMENTED_YET();
+    }
+
+    expr_ref_vector rotate_get_flips(expr* lit, expr* v, model& mdl, unsigned xx) {
+        NOT_IMPLEMENTED_YET();
+        return expr_ref_vector(m);
+    }
+
+
+};
+
+smtmus::smtmus(solver& s) {
+    m_imp = alloc(imp, s);
+}
+
+smtmus::~smtmus() {
+    dealloc(m_imp);
+}
+
+unsigned smtmus::add_soft(expr* lit) {
+    return m_imp->add_soft(lit);
+}
+
+ 
+lbool smtmus::get_mus(expr_ref_vector& mus) {
+    return m_imp->get_mus(mus);
+}
+
diff --git a/src/solver/smtmus.h b/src/solver/smtmus.h
new file mode 100644
index 000000000..7445d37e4
--- /dev/null
+++ b/src/solver/smtmus.h
@@ -0,0 +1,46 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    smtmus.h
+
+Abstract:
+   
+    MUS extraction with model rotation.
+
+Author:
+
+    Jaroslav Bendik, Nikolaj Bjorner (nbjorner) 2021-12-20
+
+Notes:
+
+--*/
+#pragma once
+
+class smtmus {
+    struct imp;
+    imp * m_imp;
+ public:
+    smtmus(solver& s);
+    ~smtmus();
+    
+    /**
+       Add soft constraint.       
+    */
+    unsigned add_soft(expr* cls);
+
+    void add_soft(unsigned sz, expr* const* clss) {
+        for (unsigned i = 0; i < sz; ++i)
+            add_soft(clss[i]);
+    }    
+
+    /**
+       Retrieve mus over soft constraints
+    */
+    lbool get_mus(expr_ref_vector& mus);
+    
+        
+};
+
+
diff --git a/src/solver/tactic2solver.cpp b/src/solver/tactic2solver.cpp
index 15c9cab82..cb381fdd9 100644
--- a/src/solver/tactic2solver.cpp
+++ b/src/solver/tactic2solver.cpp
@@ -24,7 +24,6 @@ Notes:
 #include "tactic/tactic.h"
 #include "solver/tactic2solver.h"
 #include "solver/solver_na2as.h"
-#include "solver/mus.h"
 
 /**
    \brief Simulates the incremental solver interface using a tactic.