penerase  -- Command, no inputs.  Abbreviation: pe
     This command tells the turtle to "lower its  eraser",  so  that  lines
     previously  drawn will be erased when retraced by the turtle.  It only
     works with the display turtle.  The commands penup, pendown, penerase,
     and  penreverse  are  mutually  exclusive; whichever was most recently
     used is the one which affects the turtle.  (Graphics  terminals  which
     cannot selectively erase lines, such as Tektronix displays, will treat
     penerase as pendown.)
