left --Command, one input. Abbreviation: lt
     The input is a number, the number of degrees of angle through which
     the turtle should turn counterclockwise. This command does not change
     the position of the turtle, but merely its heading (the direction in
     which it points). The turn will be only approximately correct for the
     floor turtle, because of mechanical errors. For the display turtle,
     the angle will be perfectly reproducible, although it may not look
     quite right on the screen because of the difference in size between
     horizontal and vertical dots. Nevertheless, a display turtle program
     will work in the sense that when the turtle is supposed to return to
     its starting point, it will do so.