towardsxy --Operation, two inputs.
     This operation applies only to the display turtle. The two inputs
     must be numbers, which are the x and y coordinates of a point on the
     TV screen. The output is a number which is the heading to which the
     turtle must be set, in order to point towards that point from its
     current position. Note: this operation does not actually move or turn
     the turtle. You must use it as the input to setheading if that is
     what you want.