Are 1+1 and 2+2 exceptional signatures?
  We prove that 1+1 and 2+2 target `spacetimes' of a 0-brane are exceptional signatures. Our proof is based on the requirement of SL(2,R) and `Lorentz' symmetries of a first order lagrangian. Using a special kind of 0-brane called `quatl', we also show that the exceptional signatures 1+1 and 2+2 are closely related. Moreover, we argue that the 2+2 target `spacetime' can be understood either as 2+2 worldvolume `spacetime' or as `1+1-matrix-brane'. The possibility that the exceptional 2+2-signature implies an exceptional chirotope is briefly outlined. 
J. A. Nieto