Change "hypothesis" to "ND hypothesis" where natural deduction is meant
Change "hypothesis" to "ND hypothesis" where natural deduction is meant

The term "hypothesis" has two different meanings, which could be confusing -
does it mean a $e statement, or a natural deduction hypothesis
(which is in-line in the middle of a proof)?  When the latter is meant,
change to "ND hypothesis" to make it clear what's meant.

metamath/set.mm,metamath/set.mm,metamath/set.mm