diff --git a/src/blackmisc/identifierlist.cpp b/src/blackmisc/identifierlist.cpp
index 984151a44..8a345b236 100644
--- a/src/blackmisc/identifierlist.cpp
+++ b/src/blackmisc/identifierlist.cpp
@@ -17,4 +17,9 @@ namespace BlackMisc
     CIdentifierList::CIdentifierList(const CSequence<BlackMisc::CIdentifier> &other) :
         CSequence<BlackMisc::CIdentifier>(other)
     { }
+
+    bool CIdentifierList::containsAnyNotIn(const CIdentifierList &other) const
+    {
+        return containsBy([&other](const CIdentifier &id) { return ! other.contains(id); });
+    }
 } // namespace
diff --git a/src/blackmisc/identifierlist.h b/src/blackmisc/identifierlist.h
index 3984fd00c..1ab02a28e 100644
--- a/src/blackmisc/identifierlist.h
+++ b/src/blackmisc/identifierlist.h
@@ -36,6 +36,9 @@ namespace BlackMisc
 
         //! Construct from a base class object.
         CIdentifierList(const CSequence<BlackMisc::CIdentifier> &other);
+
+        //! This list contains an identifier which is not contained in other.
+        bool containsAnyNotIn(const CIdentifierList &other) const;
     };
 } //namespace