MathDB

(MON 3)

Let

A_k (1 \le k \le h)

n-

element sets such that each two of them have a nonempty intersection. Let

A

be the union of all the sets

A_k,

and let

B

be a subset of

A

such that for each

k (1\le k \le h)

the intersection of

A_k

and

B

consists of exactly two different elements

a_k

and

b_k

. Find all subsets

X

of the set

A

with

r

elements satisfying the condition that for at least one index

k,

both elements

a_k

and

b_k

belong to

X

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