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Gruber P. Convex and Discrete Geometry

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The formula to calculate the Jordan measure in Sect. 7.2 shows that<br />

lim<br />

p→∞<br />

p prime<br />

#G p<br />

p<br />

d = 1 > V (S) + V (T ) = lim<br />

p→∞<br />

p prime<br />

26 The Torus Group E d /L 403<br />

#(S ∩ G p)<br />

p d<br />

+ lim<br />

p→∞<br />

p prime<br />

#(T ∩ G p)<br />

pd .<br />

This, in turn, implies that #(S ∩ G p) + #(T ∩ G p) ≤ #G p for all sufficiently large<br />

primes p. The lemma then shows that<br />

Thus,<br />

# � (S + Z d T � ∩ G p) ≥ #(S ∩ G p) + #(T ∩ G p) − #Hp for all<br />

sufficiently large primes p, with Hp a proper sub-group of G p.<br />

V (S + Z d<br />

≥ lim<br />

p→∞<br />

p prime<br />

T ) = lim<br />

p→∞<br />

p prime<br />

#(S ∩ G p)<br />

p d<br />

= V (S) + V (T ),<br />

# � (S +<br />

Zd T ) ∩ G �<br />

p<br />

p d<br />

#(T ∩ G p)<br />

+ lim<br />

p→∞ p p prime<br />

d<br />

− lim<br />

p→∞<br />

p prime<br />

p d−1<br />

concluding the proof of Proposition (12) <strong>and</strong> thus of Statement (ii). ⊓⊔<br />

26.3 Kneser’s Transference Theorem<br />

It is to Jarník’s credit that he first proved a transference theorem. In the subsequent<br />

development more refined tools <strong>and</strong> ideas led to further transference theorems. We<br />

mention, in particular, Hlawka’s [513] transference theorem which he proved using<br />

the method of the additional variable <strong>and</strong> Kneser’s [601] transference theorem which<br />

is based on the sum theorem. Both relate the packing <strong>and</strong> the covering radius of an<br />

o-symmetric convex body with respect to a given lattice.<br />

In this section Kneser’s transference theorem is proved. We use notions <strong>and</strong> simple<br />

properties of lattice packing <strong>and</strong> covering; see Sects. 30.1 <strong>and</strong> 31.1.<br />

For more information the reader is referred to [447].<br />

The Transference Theorem of Kneser<br />

As a consequence of the sum theorem, Kneser [601] proved the following result,<br />

where for the definitions of the packing radius ϱ(C, L) <strong>and</strong> the covering radius<br />

µ(C, L) see Sect. 23.2. The transference theorem relates lattice packing <strong>and</strong> covering.<br />

Theorem 26.2. Given an o-symmetric convex body C <strong>and</strong> a lattice L in Ed <strong>and</strong> let<br />

�<br />

d(L)<br />

(1) q =<br />

ϱ(C, L) d �<br />

d(L)<br />

<strong>and</strong> r =<br />

V (C) ϱ(C, L) d − q.<br />

V (C)<br />

Then<br />

(2) µ(C, L) ≤ ϱ(C, L)(q + r 1 d ).<br />

p d

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