1.Nounan event associated with a given infinite sequence
Y
=
{
y
k
|
k
≥
k
0
}
{\displaystyle Y=\{y_{k}|k\geq k_{0}\}}
that is determined by any subsequence of the form
Y
n
=
{
y
k
|
k
≥
n
}
,
n
≥
k
0
{\displaystyle Y_{n}=\{y_{k}|k\geq n\},n\geq k_{0}}
(a "tail" of that sequence)