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Gruber P. Convex and Discrete Geometry

Gruber P. Convex and Discrete Geometry

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252 <strong>Convex</strong> Polytopes<br />

d 2 inequalities xij ≥ 0. Now let V = (vij) beavertexof�d. By Proposition 14.1<br />

V is the intersection of dim �d = (d − 1) 2 defining support planes of �d. Thus<br />

vij = 0forsome(d − 1) 2 entries of V . The doubly stochastic matrix V cannot have<br />

a row consisting only of zeros <strong>and</strong> if every row would contain at least two non-zero<br />

entries, V would contain at most d(d − 2) 0 the hyperplane<br />

HG ={x : (u + δv) · x = 0}

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