If a block that would be discarded under previous rules becomes accepted after a rule addition, there is no reason to not simply call the new rule a hard fork. IOW it's perfectly rational to consider a weaker block as "invalid" relative to the strong chain. As such I don't see any reason to qualify the term, it's a hard fork. But Peter's observation (the specific behavior) is ultimately what matters.

e

On Nov 6, 2017, at 12:30, Paul Sztorc via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

+1 to all of Peter Todd's comments

On Nov 6, 2017 11:50 AM, "Peter Todd via bitcoin-dev" <bitcoin-dev@lists.linuxfoundation.org> wrote:
On Wed, Nov 01, 2017 at 05:48:27AM +0000, Devrandom via bitcoin-dev wrote:

Some quick thoughts...

> Hi all,
>
> Feedback is welcome on the draft below.  In particular, I want to see if
> there is interest in further development of the idea and also interested in
> any attack vectors or undesirable dynamics.
>
> (Formatted version available here:
> https://github.com/devrandom/btc-papers/blob/master/aux-pow.md )
>
> # Soft-fork Introduction of a New POW

First of all, I don't think you can really call this a soft-fork; I'd call it a
"pseudo-soft-fork"

My reasoning being that after implementation, a chain with less total work than
the main chain - but more total SHA256^2 work than the main chain - might be
followed by non-supporting clients. It's got some properties of a soft-fork,
but it's security model is definitely different.

> ### Aux POW intermediate block
>
> Auxiliary POW blocks are introduced between normal blocks - i.e. the chain
> alternates between the two POWs.
> Each aux-POW block points to the previous normal block and contains
> transactions just like a normal block.
> Each normal block points to the previous aux-POW block and must contain all
> transactions from the aux-POW block.

Note how you're basically proposing for the block interval to be decreased,
which has security implications due to increased orphan rates.

> ### Heaviest chain rule change
>
> This is a semi-hard change, because non-upgraded nodes can get on the wrong
> chain in case of attack.  However,

Exactly! Not really a soft-fork.

--
https://petertodd.org 'peter'[:-1]@petertodd.org

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