GF The Sierpiński arrowhead curve draws an equilateral triangle with triangular holes at equal intervals. It can be described with two substituting production rules: (X —> +FY-FX-FY+) and (Y —> -FX+FY+FX-. X and Y recur and at the bottom do the same thing — draw a line. Plus and minus (+ and -) mean turn 60 degrees either left or right. The terminating point of the Sierpiński arrowhead curve is always the same provided you recur an even number of times and you halve the length of the line at each recursion. If you recur to an odd depth (order is odd) then you end up turned 60 degrees, at a different point in the triangle.
L-system: Angle 60 Axiom FX F —> Z X —> +FY-FX-FY+ Y —> -FX+FY+FX- music: Piano duet Marek i Wacek plays "Military march in D major"
