I've found lots of (more or less precise) definitions of the Alexandrov curvature, but I'm mainly interested in that of "Alexandrov curvature bounded below". Could anyone give me that or give me a reference?
Thanks in advance, Valerio
I've found lots of (more or less precise) definitions of the Alexandrov curvature, but I'm mainly interested in that of "Alexandrov curvature bounded below". Could anyone give me that or give me a reference? Thanks in advance, Valerio 


From "A.D. Alexandrov spaces with curvature bounded below", Burago, Y. and Gromov, M. and Perel'man, G., Russian Mathematical Surveys, 47, 1992, p.5:
(Here $\tilde \angle pqr$ is the angle at the vertex $\tilde q$ of the triangle $\tilde \triangle pqr$ on the twodimensional "$k$plane" of curvature $k$, which has side lengths $pq$, $qr$, $rq$.) They say in the Introduction, p.1,


