Hi,
If you have difficulty understanding Exercise 3 in Assignment 1,
you may download it again as I have reworded it.
Basically, I use a* for the set {a^n | n = 0, 1, 2, ...}
and a^n for the word a...a that consists of n a's in a row.
For instance, a^4 is aaaa.
--Hongwei
(This is a message for class 20-ECES-670-2)