{{historical}}
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 Meta:DynamicPageList.
The {{tl|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?
==See also==
* Talk:List_of_sailors/Archived_feature_proposal
* Meta:Categorization#Intersection
* Meta:Category_math
* Mediazilla:5244 : Allow searching in intersections, etc. of categories.
* Meta:DynamicPageList an alternative implementation used on Wikinews.
* Meta:DynamicPageList2 a variation on the above.
==External links==
* CatScan (example)
* wikisign, make custom SQL queries (including for this proposal)