  This paper begins with an exposition of the author's research on the category
of BP_*BP-comodules, much of which is joint with Neil Strickland. The main
result of that work is that the category of E(n)_*E(n)-comodules is equivalent
to a localization of the category of BP_*BP-comodules (the localization is L_n,
analogous to the topological L_n).
  The main new result in this paper is that, analogously, the stable homotopy
category of E(n)_*E(n)-comodules is equivalent to a localization (the finite
localization L_n^f this time, not L_n) of the stable homotopy category of
BP_*BP-comodules. These stable homotopy categories were constructed in previous
work of the author, and are supposed to model stable homotopy theory; it is
like stable homotopy theory where there are no differentials in the
Adams-Novikov spectral sequence. Our result embeds the Miller-Ravenel and
Hovey-Sadofsky change of rings theorems as special cases of more general
isomorphisms.
