OK, we're all discussing this without the log. Let's see what the log has to say!

http://dom.retrobox.eu/?/20130611/log.5113bc4be4b06719e45f163f.1370945950365.txtTurn 16: All players buy a Province, putting the split at 2/2/2.

Turn 17:

P1 plays Possession and buys a Province to give 3/2/2. He draws 5 cards, and sees that he can't make a Province buy his next turn from his hand. He can, however, upgrade Potions into Duchies if P3 uses Governors.

P1 Possesses P2, and sees he can only get a Gold. He plays the Possession, giving P2 control of P3's next hand.

P2 plays his regular turn (is that the right order?), and buys a Province, making the split 3/3/2.

P2 Possesses P3 (ashersky), uses Governors to get two Provinces and an Estate. He also gets Potion->Duchy from his own hand, and P1 gets 2x Potion -> Duchy. The split is now 3(+2D)/5(+1D)/2.

P3 (ashersky) is able to get a Province, then quits (form 3rd place).

OK, now let's rewind. Pretend P1 had

*not* played P2's Possession. The sequence is:

P1 plays Possession and buys a Province. The split is 3/2/2, with no chance of P1 getting a Province next round.

P1 Possesses P2, doesn't play the Possession, and buys a Gold.

P2 plays his regular hand, buying a Province. The split is now 3/3/2.

P3 plays his hand, and uses Governors. He gains two Provinces. P1 gains 2 Duchies, and P2 gains 1 Duchy. The split is now 3(+2D)/3(+1D)/4.

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One last data point: Ashersky, when making this thread, did not have access to the knowledge that P1 wouldn't have been able to get a Province on the next round; nor did P1 know what P2 would be able to do when he played P2's Possession.

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In case 1, P1 ends up behind P2 by quite a lot. In fact, P2's lead is almost certainly insurmountable from P1's perspective, as he knows he won't get a Province next turn. In case 2, P1 ends up

*ahead of P2*.

In other words, if P1 was assuming P3's deck was much better than his own, P1's play of P2's Possession was deliberate kingmaking.