1. The Towers of Hanoi problem;Buneman;Inform. Process. Lett.,1980
2. Predicate Calculus and Program Semantics;Dijkstra,1990
3. A Logical Approach to Discrete Math;Gries,1993
4. The Magical Maze;Stewart,1997
5. Logic, Semantics, Metamathematics, Papers from 1923 to 1938;Tarski,1956