Re: Bitcoin XT - Officially #REKT (also goes for BIP101 fraud)
The definition of an "alt coin" that I like is the one based off Satoshi's description on page 3 of the Bitcoin white paper:
I summarize this as: "Bitcoin is the longest chain composed (exclusively) of valid transactions."
With that definition, a coin is "not Bitcoin" if:
(a) it's based on a blockchain that doesn't begin from the Satoshi genesis block,
(b) the blockchain does begin from the Satoshi genesis block but is not the longest chain composed of valid transactions.
I summarize this as: "Bitcoin is the longest chain composed (exclusively) of valid transactions."
With that definition, a coin is "not Bitcoin" if:
(a) it's based on a blockchain that doesn't begin from the Satoshi genesis block,
(b) the blockchain does begin from the Satoshi genesis block but is not the longest chain composed of valid transactions.
With that definition, there have been times in the past when Bitcoin was "not Bitcoin".
How so? Are you referring to times when a shorter chain eventually becomes longer than another chain? Indeed, this happened with the LevelDB bug fork in 2013 (and sort of happens almost daily if you count orphans). Perhaps it is better to say that the "longest persistent chain composed of valid transactions is Bitcoin."
How would you best define Bitcoin? And how would you best define an alt-coin, Holliday?
You answered your own question. Perhaps it is better to add "persistent", although that means we get to argue the length of persistent.
I would argue the "valid transactions" part, because valid transactions are determined by the software itself. It's almost like using a word in it's own definition. I guess it's in there to throw node operators a bone, since without it, miners themselves would decide what is "Bitcoin"!
I don't have a suitable definition for Bitcoin or alt-coin, although I'm happy to make observations on what other people think.