wikipedia on Combinatory logic
reading Combinatory logic. Quite lousy a article.
When a subject matter is esoteric, such as this, especially programing related article, typically the Wikipedia article is a hodgepodge of terms and concepts. It's like, one student added one sentence here, another student adds another term there. Nobody really understands the subject as a whole, and have zero understanding of the field's context, development, and place in ontology, but they just add and edit stuff piecemeal.
Usually, you can't say one specific sentence or place is wrong, but the whole thing together is incoherent incomprehensible crap. Though, it does get better over the years.