The invention relates to a method for operating a parking assistance system for a vehicle, comprising at least one distance sensor that detects at least sections of the lateral immediate vicinity of the vehicle and at least one path sensor that detects the path travelled by the vehicle. When one of said switching systems notifies that the first terminal is called from a second terminal, the service control point sends an incoming notification message to the first terminal through the gateway by referring the user information management table. This catalyst is then cascaded and re-used in the direct coal liquefaction process, first in the low temperature Stage 1, and then re-used in the high temperature Stage 2.