A Proven New Yorker

A quiet little man was brought before a judge. The judge looked down
at the man and then at the charges and then down at the little man in
amazement.

"Can you tell me in your own words what happened?" he asked the man.

"I'm a mathematician dealing in the nature of proof."

"Yes, go on," said the astounded judge.

"Well, I was at the library and I found the books I wanted and went
to take them out.  They told me my library card had expired and I had
to get a new one.  So I went to the registration office and got in
another line.  And filled out my forms for another card.  And got back
in line for my card."

"And?" asked the judge.

"And he asked 'Can you prove you're from New York City?' 
....So I stabbed him!"