1. Sudokuhttps://www.britannica.com/topic/sudoku
2. Sudoku as a SAT Problem;Lynce;ISAIM,2006
3. Sudoku Solving Techniqueshttp://www.sudoku9x9.com/sudoku_solving_techniques_9x9.html
4. From Frege to Gödel: A Source Book in Mathematical Logic, 1879–1931;Van Heijenoort,2002
5. First-Order Logic and Automated Theorem Proving;Fitting,2012