Math proves often start with "let". For example:
Let A be a set.
This is easy. But what about introducing several things in that manner?
- Let A be a set, B be a group, and C be a number.
- Let A be a set, let B be a group, and let C be a number.
- Let A be a set, B be a group, and let C be a number.
- Let A be a set, B a group, and C a number.
Which is the most correct one?