Proof of transfer (PoX): Stacks sees #bitcoin as the necessary ultimate proof of work, and doesn't care to duplicate it or use human-perverted PoS. Stacks uses $BTC itself as the proof of work, the skin in the game to mine blocks.
Stacks miners pay high fees to bitcoin miners. As part of the mining process, @Stacks miners compete to mine Stacks blocks by spending more bitcoin and paying high fees to bitcoin miners to anchor Stacks data on #bitcoin timechain. This helps support #bitcoin miner fee market.
