BPS preons and M-theory

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\'BPS preons were conjectured (PRL 86, 4451 (2001), hep-th/0101113) as the basic constituents of M-theory; they are states preserving 31/32 supersymmetries. We discuss the absence of preonic solutions in D=10,11 supergravities and its possible implications. The AdS generalization of the BPS preons, the AdS preons defined over an AdS vacuum, will also be discussed. This leads to the {it AdS-M-algebra}, a deformation of the M-algebra which is identifed as $osp(1|32)$.\'