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.)