> The article shows this graphically, but there is no formal proof (although the Adler & Tanton paper is mentioned).
Well, if that interested you, you could have downloaded the paper and read it. To me your comment sounds a shade entitled, as if the blog author is under an obligation to do all the work. Sometimes one has to do the work themselves.
If the author had provided links to explanations or additional materials for those who want to understand the formal reasoning more deeply.
And why does the linked paper not qualify as such a link?
P.S. Sorry, I was wrong.
Good point. I just thought that a direct link or summary of the formal reasoning would have made it easier for readers unfamiliar with the topic. But fair enough, the linked paper does cover it.