Should one include a long standard proof of a small lemma in a paper?

Question

I have a three page induction proof which is pretty typical but unusually long due to the nature of the formulae. Should it be included in a paper which probably won't exceed more than 30 pages?

Answer 1

Put it in an appendix, with a reference in the text saying that it's routine. Perhaps a reasonably small example would convince the reader to believe you without checking the proof.

If you send it to a journal you could ask in a cover letter to the editor about including it.

Last suggestion. Perhaps if you stare longer at the theorem you may find a more conceptual less tedious proof.

Answer 2

You could put it in an annex, and just have an excerpt of the proof just after the lemma to no disrupt the flow of your paper.

But people interested can still find and reference it if needed.

The issue if you do not include it somehow, is that is will become a lost proof as time goes by.