There was a young man who said, "God 
Must think it exceedingly odd 
If he finds that this tree 
Continues to be 
When there's no one about in the Quad." 

God's Reply: 

Dear Sir, Your astonishment's odd: 
I am always about in the quad 
And that's why the tree 
Will continue to be, 
Since observed by 
       Yours faithfully, God.