cr x 2
cr y 1
to
cr z 2
to
req R1
to
req R1
de z
rel R1
de x

init
cr x 1
cr p 1
cr q 1
cr r 1
to
req R2
to
req R3
to
req R4
to
to
req R3
req R4
req R2
to
de q
to
to
quit