Content update and error correction. The following is the difference between the second edition and the third edition of Discrete Mathematics published by xidian university:

1. Content update: Compared with the second edition, the third edition has been updated and improved. Discrete mathematics is a rapidly developing subject field, and new theories and methods have been introduced and discussed more comprehensively in the third edition. New mathematical models, algorithms, application scenarios, etc. There is a more in-depth and comprehensive explanation in the third edition.

2. Error correction: The third edition corrected the errors or inaccuracies in the second edition. According to the feedback from readers and teachers, after careful examination and revision, the third edition provides more accurate and reliable content.