So proof of existence, using your brain. It's always a good idea to use your brain every day. Keep it active.
所以存在的证明，用你的大脑。 每天动动脑子总是一个好主意。 保持活跃。
英语百科
Proof of Existence
Proof of Existence is an online service that verifies the existence of computer files as of a specific time via timestamped transactions in the bitcoin blockchain.
It was launched in 2013 as an open source project. It was developed by Manuel Araoz and Esteban Ordano.