We note that the essential idea of inflation, that the universe underwent a
brief period of accelerated expansion followed by a long period of decelerated
expansion, can be encapsulated in a "closure condition" which relates the
amount of accelerated expansion during inflation to the amount of decelerated
expansion afterward. We present a protocol for systematically testing the
validity of this condition observationally.Comment: 4 pages, 2 figures, matches Phys. Rev. Lett. versio