def setup():
    size(729, 729)
    fill(0)
    background(255)
    noStroke()
    rect(width / 3, height / 3, width / 3, width / 3)
    rectangles(width / 3, height / 3, width / 3)

def rectangles(x, y, s):
    if s < 1: return
    xc, yc = x - s, y - s
    for row in range(3):
        for col in range(3):
            if not (row == 1 and col == 1):
                xx, yy = xc + row * s, yc + col * s
                delta = s / 3
                rect(xx + delta, yy + delta, delta, delta)
                rectangles(xx + s / 3, yy + s / 3, s / 3)