## Dragon curve (1)

The dragon curve is a classical example of recursive method.

The definition of this curve is the following:
the dragon curve of order 1 is a vector between to arbitrary points P and Q,
the dragon curve of order n is the dragon curve of order n-1 between P and R, followed by the same curve of order n-1 between Q and R, where PRQ is an isosceles triangle with angle R being a right angle, and R being at the right of the PQ vector. Thus, if P and Q coordinates are (x, y) and (z, t), the coordinate (u, v) of R are given by:

    u = (x + z)/2 + (t - y)/2
    v = (y + t)/2 - (z - x)/2

The prototype of the method drawing the curve is the following:

    [!java|c]void [/!]dragon([!java|c]int [/!]order[!scala]:Int[/!], [!java|c]double [/!]x[!scala]:Double[/!], [!java|c]double [/!]y[!scala]:Double[/!], [!java|c]double [/!]z[!scala]:Double[/!], [!java|c]double [/!]t[!scala]:Double[/!])

You should use the method `setPos(x,y)` to put your turtle at coordinates (x,y) and the method `moveTo(z,t)` to draw a line between the turtle position and the point(z,t).

Have a look at each world's objective view to understand how to write the function.