turtle --Command, one input. Abbreviation: tur
     The input is the name of a turtle. You can only control one turtle at
     a time, so using this command a second time releases the turtle
     previously selected. The names of floor turtles are numbers like 0
     and 1. If you are using a graphics display terminal (not just a text
     display trminal), you can control the display turtle by using the word
     display (or the abbreviation dpy) as the turtle name. (As usual, the
     word must be preceded by a quotation mark.) If you use a graphics
     primitive without selecting a turtle, Logo assumes that you want to
     use the display turtle. But once you select a floor turtle, you must
     say turtle "display explicitly to switch to the display.

     The word off as input to the turtle command releases a floor turtle,
     if you have one, or turns off the graphics display if you have been
     using the display turtle. This also happens when you leave Logo.