P subject is stored as "proposition" for `@official` and "predicate" for everything else

[mi2ebi]

this is an issue instead of a pr because idk which of the two we want to keep

[dembim]

My general opinion is that official and unofficial data should be kept as similar as possible, so I suggest changing one or the other. I like "predicate" better than "proposition" for a subject type, so if all else is equal, I'd lean toward saying "change official".