Sure, some clearing brokers might have a T+1 on their prop books, so they might have arb'ed their way in today. But what happens on Thursday?
One choice - Ranbaxy spot goes to 400, to meet the future price. This is what many people are hoping, so they've gone and shorted the Sep future, to hedge the long Ranbaxy they would have taken in the spot and submitted shares.
Yet, I'm not sure - the open offer may end tomorrow, but the shares stay locked till Sep 17. Given that practically every Ranbaxy shareholder would've submitted shares for the offer - and who wouldn't, at an offer of 737 per share - there won't be much shares available for selling in the market.
Okay first law of supply and demand: If there is any demand, and supply is less, prices are going up.
If Ranbaxy goes to even 600 before Sep 17, there's literally no stopping it. If it goes up a lot it will trigger margin calls for the guys that arb'ed this deal - and that will ensure further buying with a short squeeze. So is Ranbaxy a short term buy?
Disclosure: I sure hope so, for I'm long it.