The head teacher calls a pupil into the office after going through the recent mathematics exam test papers. "You've been copying your friend's answers in the test, haven't you?" "No, I have not" replied the pupil.
"Very well," said the teacher, placing the two test papers in front of the pupil "Turn to question 26 of your friend's test paper... to which he gave the answer 'I don't know'".
"Now turn to question 26 on your test paper, to which you gave the answer 'Neither do I'.