Consider the following steps in a three$-$processor PRAM. Explain the effect of each instruction for each of the following models. Note that some instruction may be illegal under certain models; indicate so$.$ All variables are in shared memory.

a$)$ EREW PRAM

b$)$ CREW PRAM

c$)$ Common$-$ CREW PRAM

d$)$ Arbitrary$-$CRCW PRAM

Show that each step of $p-$processor Common$-$CRCW PRAM is also valid for $p-$processor arbitrary$-$CRCW PRAM.