“…Green [5] found a famous formula on Ringel-Hall numbers, usually called Green's formula, to show the bialgebra structure of the Ringel-Hall algebra and then generalized the Ringel's result to any type case. These works have led to extensive research into Ringel-Hall algebras, and a great deal of progresses has been made, see for example [18,15,6,23,21,7,13,14,9,19,20,2,22,24,8,25,1,3,4].…”