On Fri, Jun 19, 2015 at 10:48 AM, <justusranvier@riseup.net> wrote:

On 2015-06-19 17:40, Jeff Garzik wrote:

Making multiple incompatible versions of a spend is a -requirement- of
various refund contract protocols.

Is there not a dedicated field in a transaction (nSequence) for express purpose of indicating when a protocol like this is in use?

No. You cannot know which is the 'right' or wrong transaction. One tx has obvious nSequence adjustments, the other - the refund transaction - may not.

Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc. https://bitpay.com/