A very special island is inhabited only by knights and knaves. Knights always tell the truth, and knaves always lie. You meet 6 inhabitants: David, Daniel, Sebastian, Victoria, Sofia, and William. "Daniel is a knight or William is a knave," David mentioned. Daniel stated, "Victoria is a knight if and only if David is a knight". Sebastian said, "William is a knave or Victoria is a knave." "William is not a knave," Victoria mentioned. "If David is a knave then Sebastian is a knave" - Sofia. William stated, "David is a knight if and only if Sofia is a knight". So who is a knight and who is a knave?
David is a knight, Daniel is a knight, Sebastian is a knave, Victoria is a knight, Sofia is a knight, and William is a knight.
(1) David is a knight
(2) Daniel is a knight
(3) Sebastian is a knave
(4) Victoria is a knight
(5) Sofia is a knight
(6) William is a knight
Assume David is a knight. No contradiction is found in their claim that Daniel is a knight or William is a knave. Assume Daniel is a knight. No contradiction is found in their claim that Victoria is a knight if and only if David is a knight. Assume Victoria is a knight. No contradiction is found in their claim that William is not a knave. Assume William is a knight. No contradiction is found in their claim that David is a knight if and only if Sofia is a knight. Assume Sofia is a knight. No contradiction is found in their claim that If David is a knave then Sebastian is a knave. Sebastian cannot be a knight, because this would contradict the claim of their own that William is a knave or Victoria is a knave. Assume Sebastian is a knave. No contradiction is found in their false claim that William is a knave or Victoria is a knave.