I recently came across the technique known as "Dwindling Value List" (it also goes by other names). If you search FMForums you will find a couple of examples that can be downloaded.

I documented the procedure because it helps me to understand techniques (hopefully to where it becomes second nature).

I am including my documentation here in a text format. Feel free to use it, correct it, amend it, etc.

-dan

Dwindling_Value_List.txt

Just remember to prepend something such as tilde and a pilcrow before the result of the List(-function since a relation on Null value won't work no matter which of kind of relation type equi or theta ...in this case would it be obvious to assume an empty field relates to all - but it is ~¶, that make the all availiable posible.

--sd