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diff --git a/src/include/nodes/multibitmapset.h b/src/include/nodes/multibitmapset.h
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+/*-------------------------------------------------------------------------
+ *
+ * multibitmapset.h
+ *	  Lists of Bitmapsets
+ *
+ * A multibitmapset is useful in situations where members of a set can
+ * be identified by two small integers; for example, varno and varattno
+ * of a group of Vars within a query.  The implementation is a List of
+ * Bitmapsets, so that the empty set can be represented by NIL.  (But,
+ * as with Bitmapsets, that's not the only allowed representation.)
+ * The zero-based index of a List element is the first identifying value,
+ * and the (also zero-based) index of a bit within that Bitmapset is
+ * the second identifying value.  There is no expectation that the
+ * Bitmapsets should all be the same size.
+ *
+ * The available operations on multibitmapsets are intended to parallel
+ * those on bitmapsets, for example union and intersection.  So far only
+ * a small fraction of that has been built out; we'll add more as needed.
+ *
+ *
+ * Copyright (c) 2022-2023, PostgreSQL Global Development Group
+ *
+ * src/include/nodes/multibitmapset.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef MULTIBITMAPSET_H
+#define MULTIBITMAPSET_H
+
+#include "nodes/bitmapset.h"
+#include "nodes/pg_list.h"
+
+extern List *mbms_add_member(List *a, int listidx, int bitidx);
+extern List *mbms_add_members(List *a, const List *b);
+extern List *mbms_int_members(List *a, const List *b);
+extern bool mbms_is_member(int listidx, int bitidx, const List *a);
+extern Bitmapset *mbms_overlap_sets(const List *a, const List *b);
+
+#endif							/* MULTIBITMAPSET_H */