Sbastien Paquet writes about the various operations possible with RSS feeds, derived from set theory:
1. Splicing (union): I want feed C to be the result of merging feeds A and B.
2. Intersecting: Given primary feeds A and B, I want feed C to consist of all items that appear in both primary feeds.
3. Subtracting (difference): I want to remove from feed A all of the items that also appear in feed B. Put the result in feed C.
4. Splitting (subset selection): I want to split feed D into feeds D1 and D2, according to some binary selection criterion on items.
Opens up interesting possibilities…