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International Contests
Czech-Polish-Slovak Match
2019 Czech-Austrian-Polish-Slovak Match
5
5
Part of
2019 Czech-Austrian-Polish-Slovak Match
Problems
(1)
Existence of a 100 disks
Source: Czech-Polish-Slovak Match 2019 P5
7/15/2019
Determine whether there exist
100
100
100
disks
D
2
,
D
3
,
…
,
D
101
D_2,D_3,\ldots ,D_{101}
D
2
,
D
3
,
…
,
D
101
in the plane such that the following conditions hold for all pairs
(
a
,
b
)
(a,b)
(
a
,
b
)
of indices satisfying
2
≤
a
<
b
≤
101
2\le a< b\le 101
2
≤
a
<
b
≤
101
:[*] If
a
∣
b
a|b
a
∣
b
then
D
a
D_a
D
a
is contained in
D
b
D_b
D
b
. [*] If
gcd
(
a
,
b
)
=
1
\gcd (a,b)=1
g
cd
(
a
,
b
)
=
1
then
D
a
D_a
D
a
and
D
b
D_b
D
b
are disjoint.(A disk
D
(
O
,
r
)
D(O,r)
D
(
O
,
r
)
is a set of points in the plane whose distance to a given point
O
O
O
is at most a given positive real number
r
r
r
.)
combinatorics