Y by
Let
be a positive integer.
is a set of
airports. For two arbitrary airports
, if there is an airway from
to
, then there is an airway from
to
. Suppose that
has only one independent set of
airports. Let the independent set
. Prove that there exists an airport
which satisfies following condition.
Condition : For two arbitrary distinct airports
, if there exists a path connecting
and
, then there exists a path connecting
and
which does not pass
.












Condition : For two arbitrary distinct airports





