A user inputs the conclusion of a paper using a client device. A server device asks the user a question about a reason to support the inputted conclusion, and the user answers the question using the client device. If the answer is not self-evident, the server device treats the received answer as a new assertion and asks the user a question about a reason to support the new assertion. The server device repeats questions until all reasons inputted by the user become self-evident. The server device displays a logical structure of the paper which indicates a logic of the paper based on the assertion and reason given by the user.