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Gruber P. Convex and Discrete Geometry

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= δ<br />

2λ2 �<br />

11 Approximation of <strong>Convex</strong> Bodies <strong>and</strong> Its Applications 213<br />

1 � �<br />

v(J<br />

i<br />

′<br />

1<br />

i )(det qi) d+1 1<br />

�<br />

� d+1<br />

d−1<br />

mni<br />

mni<br />

mn1 +···+mnl<br />

× (mn1 +···+mnl)<br />

≥ δ<br />

2λ2 �<br />

1<br />

mn1 +···+mnl<br />

× (mn1 +···+mnl)<br />

= δ<br />

2λ2 �<br />

�<br />

≥<br />

≥<br />

δ<br />

i<br />

d+1<br />

2+<br />

2λ d−1<br />

δ<br />

d+1<br />

2+2<br />

2λ d−1<br />

�<br />

v(J ′<br />

1<br />

i )(det qi) d+1<br />

⎛<br />

⎜<br />

�<br />

�<br />

⎝<br />

⎛<br />

⎝<br />

i<br />

�<br />

bd C<br />

J ′<br />

i<br />

i<br />

v(J ′<br />

1<br />

i )(det qi) d+1 1<br />

� d+1<br />

d−1<br />

mni<br />

mni<br />

� d+1<br />

d−1<br />

κC(u) 1<br />

d+1 du<br />

⎞<br />

⎟<br />

⎠<br />

κC(x) 1<br />

d+1 dσ(x)<br />

1<br />

(mn1 +···+mnl) 2<br />

d−1<br />

d+1<br />

d−1<br />

In the second step it will be shown that<br />

(14) δ V (C, P c ⎛<br />

3d+2 �<br />

λ d−1 δ<br />

(n) ) ≤ ⎝<br />

2<br />

for all sufficiently large n.<br />

bd C<br />

⎞<br />

⎠<br />

1<br />

n 2<br />

d−1<br />

d+1<br />

d−1<br />

1<br />

n 2<br />

d−1<br />

κC(x) 1<br />

d+1 dσ(x)<br />

for all sufficiently large n.<br />

⎞<br />

⎠<br />

d+1<br />

d−1<br />

1<br />

n 2<br />

d−1<br />

By the same argument as at the beginning of the proof of (4), we may dissect bd C<br />

into finitely many pieces Ki, i = 1,...,l, <strong>and</strong> choose slightly larger sets Li where<br />

Ki ⊆ Li in bd C, points pi with neighbourhoods Ui in bd C, support hyperplanes<br />

Hi of C at pi, functions fi, quadratic forms qu = qpi u, qi = qpi pi such that the<br />

following statements hold:<br />

(15) The sets Ki are compact sets which dissect bd C, K ′ i ⊆ L′ i<br />

Jordan measurable, L ′ i is open <strong>and</strong> U ′<br />

i convex<br />

(16) v(L ′ i ) ≤ λv(K ′ i )<br />

(17) Propositions (6) <strong>and</strong> (8) hold<br />

⊆ relint U ′<br />

i are<br />

Next, convex polytopes Qn will be constructed, for all sufficiently large n, which<br />

have at most n facets <strong>and</strong> are circumscribed to C. Let<br />

�<br />

(18) τi = κC(x) 1<br />

⎛<br />

�<br />

d+1 dσ(x) ⎝ κC(x) 1<br />

⎞−1<br />

d+1 dσ(x) ⎠ , mni =⌊τin⌋.<br />

Then<br />

Ki<br />

(19) mni →+∞as n →∞<br />

bd C

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