Asnina, Erika; Osis, Janis & Jansone, Asnate (2013). "Formal Specification of Topological Relations". Databases and Information Systems VII. 249 (Databases and Information Systems VII): 175. doi:10.3233/978-1-61499-161-8-175.
"Meanings, in this sense, are often called intensions, and things designated, extensions. Contexts in which extension is all that matters are, naturally, called extensional, while contexts in which extension is not enough are intensional. Mathematics is typically extensional throughout." Stanford University primer, 2006.
