One day the King decided that he would force all his subjects to tell the
truth.  A gallows was erected in front of the city gates.  A herald
announced,
"Whoever would enter the city must first answer the truth to a question
which will be put to him."  Nasrudin was first in line.  The captain of the
guard asked him, "Where are you going?  Tell the truth -- the alternative
is death by hanging."
    "I am going," said Nasrudin, "to be hanged on that gallows."
    "I don't believe you."
    "Very well, if I have told a lie, then hang me!"
    "But that would make it the truth!"
    "Exactly," said Nasrudin, "your truth."