On 1 October 2016 at 08:02, Luke Dashjr via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

On Saturday, October 01, 2016 4:01:04 AM Rusty Russell wrote:

> - Otherwise <bits> of hash is compared to lower <bits> of blockhash.

Lower in what endian? Why only that endian? Why only lower? I can see a
possible use case where one wants to look at only the high bits to ensure
their transaction is only valid in a block with at least a certain
difficulty...

Why not use segwit versioning for all this stuff? That lets you re-enable the bitwise operations like OP_AND, permitting arbitrary bit-masks. Further, the "at least a certain difficulty" problem suggests a solution by extending the validity of opcodes like OP_LESSTHAN etc. to 256-bit inputs.