Wikipedia:Category math feature

See: Category intersection for a more recent proposal.

This is a proposal advocating the implementation of category math feature to the MediaWiki software on the English Wikipedia. Category math feature allows Wikipedians to list categories by intersection, union and subtraction. A typical Wikipedia user could find the intersection of two or more categories to be useful and efficient.

Examples:
 * Category:Guyanese actors → Category:Guyanese people & Category:Actors
 * Category:Actors by nationality would no longer be needed
 * Category:Actors / Category:Actresses → Category:Actor / Category:Male person / Category:Female person
 * Category:Child actors by nationality → Category:Child actors / Category:Actors / Category:Male person / Category:Female person / Category:Guyanese people
 * Category:Living people & Category:Golfers → Living golfers

The concern for this well favoured top-level concept would be how it would be implemented; how it would affect the performance of the live Wikipedia.

Wikinews have already implemented something like it with DynamicPageList.

The child actor birth date template automatically categorizes actors into:
 * actors who are currently children (under 13)
 * teenaged actors (13 to 19)
 * former child actors (over 19)

Category math syntax
What are the actual specifications for the category math syntax?