I'm looking for a comprehensive reference to  existing proofs of Rokhlin's theorem that a 4-dimensional closed spin PL manifold has signature divisible by 16.
I'm specifically interested in direct proofs (if any such exist) which do not rely on the fact that $\pi_i(PL/O)=0$ for small $i$.

The most commonly cited reference seems to be the book by  Kirby "The Topology of 4-manifolds". But the proof there is for smooth manifolds and I'm not sure why it works for PL manifolds although I've seen it claimed in various places that it does. The same is said about Rokhlin's original proof but I don't know why that's true either. I would also like to know if other proofs for PL manifolds exist. I'm particularly interested to know if there is a PL proof based on the Atiyah-Singer index theorem.       


Question: build email notification sytem that send emails on sql server triggers
Answer: It is a good idea, but wave you looked at what's already there, out-of the box? sp_send_dbmail does pretty much the same. It puts the mail request in a queue and uses an external application to do the SMTP stuff. I reckon that if you must use Amazon SNS then the built-in Database Mail will not work. 

Do not listen to advice that recommends sending the email directly from trigger (eg. using SQLCLR). Beside the obvious performance hit (every DML operation on the table now has to wait for the huge latency of a SMTP or HTTP operation) you have the much bigger problem of transactional consistency, how do you recall the email on rollback? So yes, using an intermediate queue is mandatory. Also have a look at Using Tables as Queues.