A crime has been committed and there are ten suspects. Precisely one of the suspects is a knight and the remaining nine are liars.
George said Arthur did it, Arthur said Bill did it, Bill said Chuck did it, Chuck said Fred did it, Eddie said Fred did it so Fred confessed and said that he did do it.
Harry said Eddie did it, Dave then confessed that he did do it- so John also confessed and said that he did it. Finally, Ian said that he didn't do it.
If George didn't do it, one of the ten suspects did do it - who committed the crime?
(In reply to re: a better solution (spoiler)
by Ady TZIDON)
Sorry, Ady, I respectfully do not concur, at least not 100%. Nobody who was accused could have done it, because the accusers are all liars. Only Harry or George could have done it. So, I will grant you three possible solutions.
George, acting alone
Harry, acting alone.
George and Harry, acting together.
I guess I do have to agree with you that "If George didn't do it, one of the ten suspects did do it" does not logically mean that George didn't do it.
Sort of like "If the Sun never rises again, then it is going to be a long night" does not imply that the Sun will never rise again.