R,R+R、R,+R,R R R rr+rrtrr R R R,R+R、R,+R,R R R R, RR 同理R R Strate Rtratr R R2R31 R1,+R2+R 闪四 西南交通大学西南交通大学 同理 3 1 2 2 3 3 1 12 R R R R R R R R + + = 1 1 2 2 3 3 1 23 R R R R R R R R + + = 2 1 2 2 3 3 1 31 R R R R R R R R + + = 12 23 31 31 12 1 R R R R R R + + = 12 23 31 12 23 2 R R R R R R + + = 12 23 31 23 31 3 R R R R R R + + =