Mathematical Poems

In the comment stream of The Greatest Physics Textbook!, a couple of mathematics poems broke out (as they are wont to do). The two examples (limerick form) were so attractive to me that I thought I'd share them with you. Also I'd rather like to hear more. I'll give you the two examples, and feel free to compose and add your own, or submit ones you've encountered elsewhere. They don't have to be limerick form. Some other standard form would be great to see too. Here they are: Torbjorn Larsson told us about this poem (which was attributed to John Saxon):