1. (10pts)

process q

var   s, exp : 0..1,     {init. 0}
      t      : integer
      c      : integer

begin
     rcv data(s,t,c) from p ->
             if exp = s ^ c = CHKSUM(s,t)  -> {accept data msg} skip;
					      exp = exp +2 1
	     [] exp != s ^ c!= CHKSUM(s,t) -> {discard data msg} skip
	     fi
end       

2. (10pts)

S = if true             -> {busy q} skip
    [] i < nr           -> akn := true
    [] nr <= i <= nr+wr -> rcvd[i mod wr], txt[i mod wr] := true, t;
			   do rcvd[nr mod wr] ->
      				send data(txt[nr mod wr]) to r;
				rcvd[nr mod wr], nr, akn := false, nr+1, true
	  	           od
    fi