Selfish Mining +Sybil attack can effectively break bitcoin incentive compatible?

[HackFisher]

http://hackingdistributed.com/2013/11/04/bitcoin-is-broken/

http://arxiv.org/pdf/1311.0243v5.pdf

The Bitcoin protocol prescribes that when a miner knows of multiple branches of the same length, it mines and propagates only the first branch it received.

This give the chance to introduce Sybil attack helping Selfish Mining to break..

And even with Sybil attack, Selfish Mining can get more revenue (relative to its ratio of hash power) with only more than 25% of hash power, which break the incentive compatible in satoshi's original paper?

I'm not sure whether I've fully understand it, but I can not find the flaw, anyone have idea about this?

Can we find a way to identify which block was mined earlier?
I also have question about the author's solution, because how can a honest miner know there will more branches in the network in the same time? Does he need to wait a while to collect all the branches? That could be a cost of some time, although not much.