A very special island is inhabited only by knights and knaves. Knights always tell the truth, and knaves always lie. You meet 6 inhabitants: Ava, Ethan, Penelope, Jack, Riley, and Sebastian. "Sebastian is not a knight," Ava declared. "Riley is a knight," Ethan mentioned. Penelope noted, "If Sebastian is a knave then Riley is a knave". Jack remarked, "Riley is a knight if and only if Sebastian is a knave". Riley was heard saying, "Sebastian is a knight if and only if Ethan is a knave". In a statement by Sebastian: "If Penelope is a knave then Jack is a knave". So who is a knight and who is a knave?
Ava is a knight, Ethan is a knight, Penelope is a knave, Jack is a knight, Riley is a knight, and Sebastian is a knave.
(1) Ava is a knight
(2) Ethan is a knight
(3) Penelope is a knave
(4) Jack is a knight
(5) Riley is a knight
(6) Sebastian is a knave
Assume Ava is a knight. No contradiction is found in their claim that Sebastian is not a knight. Sebastian cannot be a knight, because this would contradict the claim of Ava that Sebastian is not a knight. Assume Sebastian is a knave. No contradiction is found in their false claim that If Penelope is a knave then Jack is a knave. Penelope cannot be a knight, because this would contradict the false claim of Sebastian that If Penelope is a knave then Jack is a knave. Assume Penelope is a knave. No contradiction is found in their false claim that If Sebastian is a knave then Riley is a knave. Assume Riley is a knight. No contradiction is found in their claim that Sebastian is a knight if and only if Ethan is a knave. Assume Ethan is a knight. No contradiction is found in their claim that Riley is a knight. Assume Jack is a knight. No contradiction is found in their claim that Riley is a knight if and only if Sebastian is a knave.