Update formal.tex

Typo
Merge pull request #709 from spearman/patch-1

Fix typo in appendix
Updated some Punctuation problems.

In English Punctuation is important for your texts, because when I see a post which have a Punctuation problem, I will never read it, and most of the people will ignore it. It's the psychology of human.

You should put comma before which
it's utility instead of utlity
Punctuation is important in the text.

Punctuation is important in the text.

I fixed 2 Punctuation problems.
Merge pull request #710 from araratm/master

Updated some Punctuation problems.
Merge pull request #711 from araratm/patch-1

Punctuation is important in the text.