SHORT VERSION: you don't need to do anything:
    if     you qualify according to the rules below,
           you will be automatically admitted
    else,  unfortunately, you will not (our apologies!)

LONG VERSION:
    In order to be fair to everybody, we strictly follow these rules
    when admitting students from the waitlist:

    (0) we only consider people who have the prerequisites
    (1) among them, we give priority to VLIS/CS-MSC, because,
        for these people, the course is mandatory
        in their program of study
    (2) and then, on first-come basis
    (3) until we reach max load for TAs, or fire-safety room capacity
        whichever is smaller.

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Christos Faloutsos, May 20, 2016