try to implement apply
try to implement apply

interesting issue: not clear how to refer to the "cur" state in
apply's loop invariant, since we no longer have ghost variables,
and the overall hoare tuple (which contains "cur") doesn't get
defined until later..

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl