Technological progress

1. Support forced removal of channels; If one party wants to make the settlement while its counterpart is not online, it will have to sign the latest transaction with both signatures on the chain before completing the unilateral forced removal of the channel.

2. Confirmation on the forced removal of channels; we added a txid-monitoring module to the trinity nodes. When one party goes on-line, it will immediately detect the forced removal by its counterpart. With the monitor, this party can then judge whether the signed transaction was the latest one, and if not, it will be entitled to submit a penalty transaction to sanction the evil-doer.