ous
    subsets of X is indeed something that changes over time.
 
JA: Anyways, this is kind of tentative,
    and may of course change with time.
 
LO: There are some additions from &quot;The duality principle ...&quot; point of view.
    They differ a &quot;subject area&quot; from a &quot;classsification field&quot;.  The first
    one is &quot;not closed&quot; class in principle.  The last is a &quot;good set&quot; when
    the proper &quot;primary&quot; identifications from real objects to &quot;minimal