The logician Raymond Smullyan describes an island containing two types of people: knights who al- ways tell the truth and knaves who always lie. Now, you are visiting the island and have the following encounters with natives. (a) Two natives A and B address you as follows: A says: Both of us are knights. B says: A is a knave. What are A and B? (b) Another two natives C and D approach you but only C speaks. C says: Both of us are knaves. What are C and D? (c) You then encounter natives E and F. E says: F is a knave. F says: E is a knave. How many knaves are there