I found several examples in affirmative construction:It doesn't mean anything, because don't use that construction.
I find that odd, and would need the surrounding context before I could see it as having any chance of being an appropriate use of "let alone".Such consequences, let alone the contamination of soil and crop, have led some farmers to adopt the so-called “rational” approach to pesticide use.
I've considered it, but it would never pass my lips, the tip of my pen, or my keyboard.Consider: My son avoids doing dishes, let alone mowing the lawn. It's positive in grammar, but negative in concept
As I said, the boy reaching the pedals is fine. My "not only but also" test where the "but also" item is clearly more extreme than the "not only" item is, I think, the same asWhat do you think of the concept, though, Andy. Grammatically positive sentence, but negative concept-- wherein 'let alone' fits.
This passes my test: "The subject is challenging at undergraduate level, let alone at postgraduate level." although I'd prefer "The subject is challenging at undergraduate level, and even more so at postgraduate level."You can perhaps think about expressions like (even) more so rather than use let alone.