Hi everyone! I just had a couple questions about a few things I read in a textbook.

There were a couple points made that did not show any proof. I was able to prove some of them but the two listed below gave me some trouble. I like to see why things are so and need the proof in order to accept its validity. I was wondering if anyone here could help me prove these?

--- If b > 1 is not prime, then (b-1)! is not congruent to -1 (mod b)

--- If p is an odd prime, then (p-3)! ≡ (p-1)/2 (mod p)

Thank You!