Rewrite and clarify some parts

[minhducsun2002]

Rephrase some parts of the license.

Also make some words stricter.

[cszach]

I agree with most of your changes. Here are some that I don't:

1. "call" and "claim" are very different, and I use the former because it is more generic, so you should just keep it.
2. I think "when", in this context, is more appropriate than "upon".
3. Change "if and only if his/her name" to "only if their name". I guess you took that "if and only if" from your Math teacher?

[minhducsun2002]

1. claim is more formal.
2. upon is more formal.
3. Yeah, be precise about words.

P/s : 1 and 2 are personal opinion.