diff --git a/src/ast/rewriter/seq_axioms.cpp b/src/ast/rewriter/seq_axioms.cpp
index b4c142e68..9ab1a067b 100644
--- a/src/ast/rewriter/seq_axioms.cpp
+++ b/src/ast/rewriter/seq_axioms.cpp
@@ -1336,6 +1336,22 @@ namespace seq {
             add_clause(emp, mk_ge_e(mk_len(s), idx));
     }
 
+    /**
+    * Consider the recursive definition of negated contains:
+      ~contains(a, b) = 
+        if |b| > |a| then true
+        else if |b| = |a| then a != b
+        else ~prefix(b, a) and ~contains(a[1:], b)
+
+        Create the recursive function not_contains that implements this recursive definition.
+        Add the axiom
+            contains(a, b) or not_contains(a, b)
+    */
+
+    void axioms::not_contains_axiom(expr *e) {
+        throw default_exception("not implemented");
+    }
+
     expr_ref axioms::length_limit(expr* s, unsigned k) {
         expr_ref bound_tracker = m_sk.mk_length_limit(s, k);
         expr* s0 = nullptr;
diff --git a/src/ast/rewriter/seq_axioms.h b/src/ast/rewriter/seq_axioms.h
index 0c29ad5d8..29fffe00f 100644
--- a/src/ast/rewriter/seq_axioms.h
+++ b/src/ast/rewriter/seq_axioms.h
@@ -113,6 +113,7 @@ namespace seq {
         void unit_axiom(expr* n);
         void length_axiom(expr* n);
         void unroll_not_contains(expr* e);
+        void not_contains_axiom(expr *e);
         void replace_re_axiom(expr* e);
         void replace_all_axiom(expr* e);
         void replace_re_all_axiom(expr* e);