Knights always tell the truth,liars always lie,and knaves alternate between truths and lies.
Two people named Jimmy and Johnny make the following claims.
Jimmy:I am a knave.
Johnny:Jimmy is not a knight.
Jimmy:Johnny is a knave.
Johnny:Jimmy is a knave.
What are each?
Jimmy's first and second statements clearly establishes him to be a Liar or Knave.
Johnny's first statement thus implies that he is a Knight.
Accodingly, by Johnny's true second statement, Jimmy is a Knave
Jimmy is a Knave.
Johnny is a Knight.