(a＼a＠-1)+(3a+1＼a＠-1)+(2a+3＼1-a＠)
=a/[(a+1)(a-1])+(3a+1)/[(a+1)(a-1)+(2a+3)/[(1-a)(1+a)]
=(a+3a+1-2a-3)/(a+1)(a-1)
=(2a-2)/(a+1)(a-1)
=2/(a+1)