// black -> white Repeat a 100 5 { Paper a } Paper 5 Pen 0 Repeat a 0 50 { Line (50+a) (50-a) (50+a) (50+a) Line (50-a) (50-a) (50-a) (50+a) Line (50-a) (50-a) (50+a) (50-a) Line (50+a) (50+a) (50-a) (50+a) }