The Rule Against Perpetuities can be simply stated as follows:

     "No interest is good unless it must vest, if at all, not
later than 21 years after some life in being at the creation of
the interest."

     The key to applying the Rule is to work through each concept
one step at a time.  We will start with the concept of vesting.
An interest is "vested" when we know for sure that someone will
receive or fail to receive the interest.
     Question 1: Elvis Presley dies, leaving a will that devises Blackacre to
his daughter Lisa Marie.  Is Blackacre vested at the time of
Elvis' death?
      YES, because we know for sure that Lisa Marie will receive
the property.
      NO, because Lisa Marie may not be alive at the time of
Elvis' death.