Page 389, fourth line: the sign of the coefficients Aij should be minus
The metric is that of a Cahen-Wallach symmetric space, whose cosetconstruction is reviewed in Section ..., with Aij= -λ2δij.
Addendum: The algebra takes the form
Page 389, Eqs. (13.96): a factor of λ is missing in the first equation
Addendum: The spinorial representation of Pv is trivial: Γs(Pv) = 0.
Page 393, Eq. (13.111): The sign of the vector field should be changed to minus and the
parameter λ6 in the 1-form ω should be divided by the square root of 2: