Nature gives the rule
Without that I've read the whole Compendium, not even the rich entries for the various editions of the Bibliotheque Oulipienne, I begin to think that the subtlest Oulipian restriction is that known as "Canada Dry":
The name of this procedure is taken from the soft drink marketed as "the champagne of ginger ales". The drink may have bubbles, but it isn't champagne; in the words of Paul Fournel, who coined the term, a Canada Dry text "has the taste and colour of a restriction but does not follow a restriction".
Not a determinate restriction, anyway (or rather, not one visible from the resulting text), but it clearly is a restriction: appear to follow a determinate rule, but actually follow none (other than this very rule). As GC Lichtenberg would say, this is a Kantian idea (except not really really). Examples:
Wand-escape ether evil draws.
"Crack legions apprehend undue assaults," said conductor of lead tank, staccato.
Franz of black fiacre aspires to Luke's matches.
Comments
on 2006-11-06 8:12:18.0, Matt Weiner commented:
To tell a long involved story that ends with an oddly stilted sentence that sounds like a pun, but is not, would be a Canada Dry pseudo-shaggy dog story, then, would it not? In case anyone had ever done or suggested such a thing.
and, further, on 2006-11-07 9:31:55.0, ben wolfson commented:
That is a good idea, Weiner, who knows that he has suggested just such a thing, but is "shaggy dog story pun" really a restriction in the proper way?