Suppose one were writing a book aimed at high-school students (and their teachers), where "high-school" in the US means grades 9,10,11,12 (where college/university starts at 13). The book is not a textbook, but rather "math enrichment." The book attempts to expose such students to proofs, and to research questions in mathematics. I have questions about the best way to cite the research questions. Here are four alternatives:
(1) With introductory explanation, treat it just like a research paper, e.g., "this was proved in [ABC99]." One point would be train students to understand such references and how to access them (increasingly easy via the Internet).
(2) Instead, use Notes, gathered at the end of each chapter, something like this,1 and then the referenced note says, 1This was proved in [ABC99]. Again, advanced explanation would be needed to interpret "[ABC99]."
(3) Have no interruptions in the text—no citations, no footnotes—but at the end of the chapter in a Notes section, explain the references and history etc, citing backwards to previous pages.
(4) Similar to (3), but have all Notes gathered at the end of the book. This seems to be the current standard in academic treatises.
I'd appreciate your opinions!