square
  is a shortcut for creating a window object
  representing the square 
  $[0,r] \times [0,r]$.
  It is equivalent to the command
  owin(c(0,r),c(0,r)).  unit.square creates the unit square
  $[0,1] \times [0,1]$.
  It is equivalent to
  square(1) or square() or owin(c(0,1),c(0,1)).
  These commands are 
  included mainly to improve the readability of some code.