It sounds like they're actually conflating the two words in question. Introductory means an introduction, like the thing that helps you get into a subject. Elem

It sounds like they're actually conflating the two words in question. Introductory means an introduction, like the thing that helps you get into a subject. Elementary means basic or foundational. Logic and set theory are elementary to the rest of mathematics. They're not introductory to the rest of mathematics.