1.Nouna pair of integers
(
i
,
j
)
{\displaystyle (i,j)}
is an inversion pair of some permutation
σ
{\displaystyle \sigma }
if
i
<
j
{\displaystyle i<j}
but \sigma (j)}">
σ
(
i
)
>
σ
(
j
)
{\displaystyle \sigma (i)>\sigma (j)}
\sigma (j)}">.