used after a statement to emphasize that because the first thing is not true or possible, the next thing cannot be true or possible either :
There isn't enough room for us, let alone any guests.
used after a statement to emphasize that because the first thing is not true or possible, the next thing cannot be true or possible either :
There isn't enough room for us, let alone any guests.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005