In a symmetric space of noncompact type X = G/K oriented
geodesic segments correspond modulo isometries to vectors in the
Euclidean Weyl chamber. We can hence assign vector valued
lengths to segments. Our main result is a system of homoge-
neous linear inequalities, which we call the generalized triangle
inequalities or stability inequalities, describing the restrictions on
the vector valued side lengths of oriented polygons. It is based on
the mod 2 Schubert calculus in the real Grassmannians G=P for
maximal parabolic subgroups P.