My father's favorite example: a sign that says "No Parking Allowed".
So, it's OK if you don't park there. But can you park there if you want to?
That's an interesting demonstration that our language is non-associative (specifically, No (Parking Allowed) != (No Parking) Allowed). It's also non-Abelian (a truncated triakis tetrahedron is not the same as a triakis truncated tetrahedron).
I've liked the roundabouts I've used in the U.K., Australia, and Boston. But the idea is to turn into the circular flow of traffic without stopping. I don't see how they can work if the traffic isn't all clockwise (in the U.K., counterclockwise in the U.S.).
It's all clockwise if you think of it as six disjoint roundabouts instead of one large compound roundabout. Theoretically, you could assemble these magic roundabouts recursively to produce an even larger clockwise one. http://en.wikipedia.org/wiki/Antoine%27s_necklace Sincerely, Adam P. Goucher http://cp4space.wordpress.com