Selects either `X0` or `X1` based on `IDX` index value.
nth-input(number)
@/nth-input(number)
Selects either `X0` or `X1` based on `IDX` index value.
OUTnumber
The selected value. Equals to one of `Xi` input.
_number
Utility output needed for expanding node. Shoud be ignored by the end user.