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Algorithm 3: proof of correctness
(cont.)
uIf Pj has set flag[j]=true
and is in its while(), then either turn=i or turn=j
uIf
turn=i, then Pi enters CS. If turn=j then Pj enters CS but will then reset
flag[j]=false on exit: allowing Pi to enter CS
ubut if Pj has
time to reset flag[j]=true, it must also set turn=i
usince
Pi does not change value of turn while stuck in while(), Pi will enter CS after
at most one CS entry by Pj (bounded waiting)