【正文】
B + D B + C + D L → C + D f =1 f =0 C + D A + C + D L → B f =2 L + B → D f =1 f =0 B + D B + C + D L → B f =2 L + B → D f =1 B + D C + D L → C + D f =1 f =0 A + C + D L → D f =2 L → B f =2 L + B → D f =1 B + D C + D f =0 A + C + D L → C + D f =1 f =0 L → B f =2 L + B → D f =1 B + D A + D L → A + D f =1 f =0 A + C + D L → D f =2