Which is the exact same function of the difference between any competitor, so you can actually fairly compare them on the lossy part.. like, people have been thinking about this problem much more than the 3 minutes HNers in this comment section.

yep!

Arithmetic coding allows you to make a prediction and only provide bits for correction.

Have the de-compressor predict the next data based on the outcome so far (a statistical prediction of next data will be lossy as it won't always be correct). If the prediction is correct you need to spend very little to confirm that. If it's incorrect you'll need to spend data to correct it. Arithmetic coding is the best way to make this work.

It's also been used by all winning entries of the Hutter prize so far.

Or at least reproducible. It could still be compressed.

What