Key node of convergence

In order to effectively connect the old and new lessons, the key is to find the joint point of connection. The effective connection between the old and new lessons is not the all-round connection without any emphasis, but the connection between the locomotive and the carriage. It is not the "complete" contact between the back face of the former and the front face of the latter, but the reinforcement after hooking. Similarly, the old and new courses are also interlinked. ...