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+OPTIONAL
+SYNOPSIS
+        mixed * intersect_alist (mixed * list1, mixed * list2)
+
+DESCRIPTION
+        Does a fast set intersection on alist key vectors (NOT on full alists!).
+        The operator '&' does set intersection on arrays in general.
+
+EXAMPLE
+        new_list = intersect_alist(list1, list2);
+
+SEE ALSO
+        filter(E), assoc(E), insert_alist(E), map(E),
+        member_array(E), order_alist(E), sort_array(E), unique_array(E)