The Robin Hood Group and Ethereum Classic

Everyone expected it to die and most hash power switched over, but not all. Enough was left that the anti-fork people started calling it classic and poloniex started trading it, probably to let people who now had ETC liquidate. But the trading wasn't a straight line to zero as most expected, the "movement" became s but real and now it is still a very large crypto currency by market cap - and hash rate- despite being the "loser".

Given how dynamic Ethereum is code wise there may well be a market for an Ethereum alternative for ETC to fill. Lisk and Expanse seem to indicate this is possible.

As it stands you got two seemingly contradicting answers to your question. They are actually both sort of correct.

You can indeed try to replay a transaction from one chain to the other. Everything in the transaction is still valid. It will be propagated by the p2p nodes as they just perform crypto sanity check.

It doesn't mean it will be included in a block though. For the replay to goes through and be included in the blockchain, there needs to be at least as many coins held by the address in the other chain. This is usually not the case for addresses created post-fork. However, all addresses that had coins before the fork are susceptible to this issue. There are guides to "split" the coins so that you can safely separate them and hold them in brand new addresses that have zero balance on the other chain.

It's a painful issue that was raised before the fork but had been downplayed by pro-fork supporters as the old chain was supposed to die quickly.

As the transaction is already signed on one chain you don't need the private key to issue the same transaction on the other.

those coins don't exist on the new ETH blockchain, so that particular transaction cannot be performed on the new block.

You have coins on both block chains now

Merry Christmas!

Just be careful, read up on replay attacks before splitting your ETH/ETC.

So you have both now.