diff --git a/sharedbits/alloc_header.h b/sharedbits/alloc_header.h
new file mode 100644
index 00000000..83b24946
--- /dev/null
+++ b/sharedbits/alloc_header.h
@@ -0,0 +1,5 @@
+// 30 may 2019
+
+#ifndef sharedbitsPrefix
+#error you must define sharedbitsPrefix before including this
+#endif
diff --git a/sharedbits/alloc_impl.h b/sharedbits/alloc_impl.h
new file mode 100644
index 00000000..bd7318d9
--- /dev/null
+++ b/sharedbits/alloc_impl.h
@@ -0,0 +1,6 @@
+// 30 may 2019
+// requires: alloc_header.h
+
+#ifndef sharedbitsPrefix
+#error you must define sharedbitsPrefix before including this
+#endif
diff --git a/sharedbits/array_header.h b/sharedbits/array_header.h
new file mode 100644
index 00000000..bd7318d9
--- /dev/null
+++ b/sharedbits/array_header.h
@@ -0,0 +1,6 @@
+// 30 may 2019
+// requires: alloc_header.h
+
+#ifndef sharedbitsPrefix
+#error you must define sharedbitsPrefix before including this
+#endif
diff --git a/sharedbits/array_impl.h b/sharedbits/array_impl.h
new file mode 100644
index 00000000..e485d5a4
--- /dev/null
+++ b/sharedbits/array_impl.h
@@ -0,0 +1,6 @@
+// 30 may 2019
+// requires: array_header.h
+
+#ifndef sharedbitsPrefix
+#error you must define sharedbitsPrefix before including this
+#endif