  Maximally supersymmetric spacetime algebras in eleven-dimensions, which are
the isometry superalgebras of Minkowski space, AdS_7 x S^4, AdS_4 x S^7 and
pp-wave background, are related by Inonu-Wigner contractions. The
super-AdS_{4(7)} x S^{7(4)} algebras allow to introduce two contraction
parameters, the one for the flat limit to the super-Poincare algebra and the
other for a Penrose limit to the super-pp-wave algebra. Under these
contractions supersymmetries are maintained because the Jacobi identity of
three supercharges holds for any values of contraction parameters.
