diff --git a/include/xo/expression2/Binding.hpp b/include/xo/expression2/Binding.hpp
index 6dffb16b..a27de6b3 100644
--- a/include/xo/expression2/Binding.hpp
+++ b/include/xo/expression2/Binding.hpp
@@ -24,6 +24,9 @@ namespace xo {
             static Binding global() { return Binding(s_link_global, 0); }
             static Binding local(int32_t j_slot) { return Binding(0, j_slot); }
 
+            bool is_null() const {
+                return (i_link_ == s_link_sentinel) && (j_slot_ == -1);
+            }
             bool is_global() const { return i_link_ == s_link_global; }
             bool is_local() const { return (i_link_ == 0) && (j_slot_ >= 0); }
 
diff --git a/include/xo/expression2/Variable.hpp b/include/xo/expression2/Variable.hpp
new file mode 100644
index 00000000..26ef649b
--- /dev/null
+++ b/include/xo/expression2/Variable.hpp
@@ -0,0 +1,13 @@
+/** @file Variable.hpp
+ *
+ *  @author Roland Conybeare, Feb 2026
+ **/
+
+#pragma once
+
+#include "DVariable.hpp"
+#include "detail/IExpression_DVariable.hpp"
+#include "detail/IGCObject_DVariable.hpp"
+#include "detail/IPrintable_DVariable.hpp"
+
+/* end Variable.hpp */