(I don’t know why the culture of pure math persists in this. I throw it in with proof by intimidation. Makes pure math types sound like they’re stuck intellectually/socially at being highly precocious 14 year olds. It’s not the individual, it’s the culture.)
Chentsov, that’s a name I haven’t heard in a long time. There’s a result that’s worth being generally known by the data analysis community. The article looks like it gets there more clearly than others I read a while ago.
This also boils down to what you understand the word "elementary" to mean. It is definitely not synonymous to "simple", rather as Feynman put it, "only requiring an infinite intelligence to understand".
If your textbook was "Advanced X for Scientists and Engineers", easy-peasy. But if the textbook was "Introductory X" you were in for it.
Addendum: What I mean is that you can get much more abstract and take many more things for granted than it's done here. It's like reading an elementary introduction to the geometry of schemes, even if it's elementary there is a bunch of stuff that has to be assumed as known, even if the explanation of schemes per se is elementary