{
    (isEmpty)(lPopped)(lItem)(rPopped)(rItem)
        [lPopped]
|
    dequeLPopped
}

{
    (isEmpty)(lPopped)(lItem)(rPopped)(rItem)
        [lItem]
|
    dequeLItem
}

{
    (isEmpty)(lPopped)(lItem)(rPopped)(rItem)
        [rPopped]
|
    dequeRPopped
}

{
    (isEmpty)(lPopped)(lItem)(rPopped)(rItem)
        [rItem]
|
    dequeRItem
}