On 11/16/2016 05:24 PM, Alex Morcos wrote:
> huh?
> can you give an example of how a duplicate transaction hash (in the same
> chain) can happen given BIP34?

"The pigeonhole principle arises in computer science. For example,
collisions are inevitable in a hash table because the number of possible
keys exceeds the number of indices in the array. A hashing algorithm, no
matter how clever, cannot avoid these collisions."

https://en.wikipedia.org/wiki/Pigeonhole_principle

e

> On Wed, Nov 16, 2016 at 7:00 PM, Eric Voskuil via bitcoin-dev wrote:
> 
>     On 11/16/2016 03:58 PM, Jorge Timón via bitcoin-dev wrote:
>     > On Wed, Nov 16, 2016 at 3:18 PM, Thomas Kerin via bitcoin-dev
>     > <bitcoin-dev@lists.linuxfoundation.org
>     <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>     >> BIP30 actually was given similar treatment after a reasonable amount of time
>     >> had passed.
>     >> https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L2392
>     <https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L2392>
>     >
>     > This is not really the same. BIP30 is not validated after BIP34 is
>     > active because blocks complying with BIP34 will always necessarily
>     > comply with BIP30 (ie coinbases cannot be duplicated after they
>     > include the block height).
> 
>     This is a misinterpretation of BIP30. Duplicate transaction hashes can
>     and will happen and are perfectly valid in Bitcoin. BIP34 does not
>     prevent this.
> 
>     e