.  Figure 00.0 shows an example where there are four processes,  , and  , where   and  . The initial configuration   is shown on the left. The top part of the figure shows an execution in which   write 0 and 0, respectively, read the array to reach  , and then   writes 0 and reads to reach  . The bottom part shows an alternative execution in which   write 0 and 0, respectively, read the array to reach  , and then   writes 0 and reads to reach  .  Figure 00.0 Proof of Lemma 00.0.0: The starting configuration   is shown on the left, where  , and each memory element is initialized to 