The poem's original publication, so far as I can tell, was in Douglas Hofstadter's wonderful* book Le Ton Beau de Marot: In Praise of the Music of Language (p. 272). Hofsdater says that James Falen (who is best known as a translator of Pushkin's novel in verse Eugene Onegin) included the poem in a letter, and describes it as "an 'odelet in praise of constraints'" -- which I think of as the poem's title, although it seems to have been given by Hofstadter, not Falen.
So, without further ado, the poem:
Every task involves constraint,A marvelous little poem, to my ears.
Solve the thing without complaint;
There are magic links and chains
Forged to loose our rigid brains.
Strictures, structures, though they bind,
Strangely liberate the mind.
-- James E. Falen
(Note: this post is my first experiment in scheduled posting. If all goes well, it should go up on Saturday, July 19, even though I'm writing it on Wednesday, July 16. We'll see...)
* Thought provoking, delightful to read, and wrong on many topics, but in a way that is fun to argue with and which leads to a lot of great other books. So, with that caveat, I recommend it highly. (Can a book you think is fundamentally wrong in its central argument be one of your favorite books? If so, this is one of mine.) An earlier version of Hofstadter's section of the book on Pushkin can be found here.