Do the given call working with imaginary dancers (i.e., Phantoms).  Assume that
  the Phantoms are in whatever position, have whatever facing direction, and are
  of whatever sex is necessary in order to execute the given call.  The call is
  then danced with both the dancers and the Phantoms participating.  Keep track
  of the Phantoms that you are working with and reserve space for them at the
  completion of the call. 
EN: 20