On Tue, 18 Jun 1996, Kergma, The Chaotic Trickster wrote:

A portrait hung in a gentleman's library.  He was asked whom it 
represented.  He replied, "Uncles and brothers have I none, but that 
man's father is my father's son."   Who was the portrait of?

"My father's son" could mean "me", or "my brother". Since he has no 
brothers, it has to mean "me".

...but that man's father is me.

So the person in the portrait is the gentleman's child.

Explain how a window can be made twice its former size, without 
increasing either its height or width.

You never said I couldn't increase its depth. :)