diff --git a/src/ast/rewriter/seq_eq_solver.cpp b/src/ast/rewriter/seq_eq_solver.cpp
new file mode 100644
index 000000000..79e111f7a
--- /dev/null
+++ b/src/ast/rewriter/seq_eq_solver.cpp
@@ -0,0 +1,92 @@
+/*++
+Copyright (c) 2011 Microsoft Corporation
+
+Module Name:
+
+    seq_eq_solver
+
+Abstract:
+
+    Solver-agnostic equality solving routines for sequences
+    
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-01
+
+--*/
+
+#include "ast/rewriter/seq_eq_solver.h"
+
+namespace seq {
+
+
+    bool eq_solver::solve(eq const& e, eq_ptr& r) {
+        if (solve_itos1(e, r))
+            return true;
+        if (solve_itos2(e, r))
+            return true;
+
+        return false;
+    }
+
+    void eq_solver::add_consequence(expr_ref const& a) {
+        m_clause.reset();
+        m_clause.push_back(a);
+        m_add_consequence(true, m_clause);
+    }
+
+    void eq_solver::add_consequence(expr_ref const& a, expr_ref const& b) {
+        m_clause.reset();
+        m_clause.push_back(a);
+        m_clause.push_back(b);
+        m_add_consequence(true, m_clause);
+    }
+
+    /**
+     * from_int(s) == from_int(t)
+     * --------------------------
+     * s = t or (s < 0 and t < 0)
+     */
+        
+    bool eq_solver::match_itos1(eq const& e, expr*& a, expr*& b) {
+        return 
+            e.ls.size() == 1 && e.rs.size() == 1 && 
+            seq.str.is_itos(e.ls[0], a) && seq.str.is_itos(e.rs[0], b);
+    }
+
+    bool eq_solver::solve_itos1(eq const& e, eq_ptr& r) {
+        expr* s = nullptr, *t = nullptr;
+        if (!match_itos1(e, s, t))
+            return false;
+        r = nullptr;
+        expr_ref eq = mk_eq(s, t);
+        add_consequence(eq, mk_le(s, -1));
+        add_consequence(eq, mk_le(t, -1));
+        return true;
+    }
+
+    /**
+     * from_int(s) == ""
+     * -----------------
+     *       s < 0
+     */
+    
+    bool eq_solver::match_itos2(eq const& e, expr*& s) {
+        if (e.ls.size() == 1 && e.rs.empty() && seq.str.is_itos(e.ls[0], s))
+            return true;
+        if (e.rs.size() == 1 && e.ls.empty() && seq.str.is_itos(e.rs[0], s))
+            return true;
+        return false;
+    }
+
+    bool eq_solver::solve_itos2(eq const& e, eq_ptr& r) {
+        expr* s = nullptr;
+        if (!match_itos2(e, s))
+            return false;
+        r = nullptr;
+        add_consequence(mk_le(s, -1));
+        return true;
+    }
+
+};
+
diff --git a/src/ast/rewriter/seq_eq_solver.h b/src/ast/rewriter/seq_eq_solver.h
new file mode 100644
index 000000000..79975d393
--- /dev/null
+++ b/src/ast/rewriter/seq_eq_solver.h
@@ -0,0 +1,75 @@
+/*++
+Copyright (c) 2011 Microsoft Corporation
+
+Module Name:
+
+    seq_eq_solver
+
+Abstract:
+
+    Solver-agnostic equality solving routines for sequences
+    
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-01
+
+--*/
+#pragma once
+
+#include "ast/rewriter/seq_axioms.h"
+
+namespace seq {
+
+    struct eq {
+        expr_ref_vector ls;
+        expr_ref_vector rs;
+        eq(expr_ref_vector& l, expr_ref_vector& r):
+            ls(l), rs(r) {}
+    };
+
+    typedef scoped_ptr<eq> eq_ptr;
+        
+    class eq_solver {
+        ast_manager& m;
+        axioms&      m_ax;
+        seq_util     seq;
+        expr_ref_vector                        m_clause;
+        std::function<expr*(expr*)>            m_value;
+        std::function<bool(expr*, rational&)>  m_int_value;
+        std::function<void(bool, expr_ref_vector const&)>  m_add_consequence;
+
+        bool match_itos1(eq const& e, expr*& s, expr*& t);
+        bool solve_itos1(eq const& e, eq_ptr& r);
+
+        bool match_itos2(eq const& e, expr*& s);
+        bool solve_itos2(eq const& e, eq_ptr& r);
+
+        void add_consequence(expr_ref const& a);
+        void add_consequence(expr_ref const& a, expr_ref const& b);
+
+        expr_ref mk_eq(expr* a, expr* b) { return expr_ref(m.mk_eq(a, b), m); }
+        expr_ref mk_ge(expr* x, int n) { return m_ax.mk_ge(x, n); }
+        expr_ref mk_le(expr* x, int n) { return m_ax.mk_le(x, n); }
+        expr_ref mk_ge(expr* x, rational const& n) { return m_ax.mk_ge(x, n); }
+        expr_ref mk_le(expr* x, rational const& n) { return m_ax.mk_le(x, n); }
+
+    public:
+        
+        eq_solver(ast_manager& m, axioms& ax):
+            m(m),
+            m_ax(ax),
+            seq(m),
+            m_clause(m)
+        {}
+
+        void set_value(std::function<expr*(expr*)>& v) { m_value = v; }
+        void set_int_value(std::function<bool(expr*,rational&)>& iv) { m_int_value = iv; }
+        void set_add_consequence(std::function<void(bool, expr_ref_vector const&)>& ac) { m_add_consequence = ac; }
+
+        bool solve(eq const& e, eq_ptr& r);
+
+        
+    };
+
+};
+