LR

PPA = (PPB, XXX)
PPB = (XXX, PPZ)
PPZ = (PPB, XXX)
QQA = (QQB, XXX)
QQB = (QQC, QQC)
QQC = (QQZ, QQZ)
QQZ = (QQB, QQB)
XXX = (XXX, XXX)