Massive gravity as a limit of bimetric gravity
  Massive gravity may be viewed as a suitable limit of bimetric gravity. The
limiting procedure can lead to an interesting interplay between the
"background" and "foreground" metrics in a cosmological context. The fact that
in bimetric theories one always has two sets of metric equations of motion
continues to have an effect even in the massive gravity limit. Thus, solutions
of bimetric gravity in the limit of vanishing kinetic term are also solutions
of massive gravity, but the contrary statement is not necessarily true.
