When I look in old mathematical textbooks from the seventies and before, mathematics is always upright. Their use of italic letters in other contexts, however, shows that this is not because of technical limits. On the other hand, all textbooks I have seen with italic math look very TeX-like. So I was wondering if this is a coincidence? could italic math be an invention by Knuth introduced in TeX?
Does someone know the history of italic math?