“…Therefore, a lot of interesting formulae, which compute the number of the BPS bound states or topological invariants, have been derived. In mathematics, topological properties of the quiver moduli spaces are investigated in [3,4] for example, and they come to fruition of the so-called "wall crossing formula" by Joyce and Song [5], and Kontsevich and Soibelman [6]. The wall crossing formula is physically interpreted and rederived in the Coulomb branch of the quiver quantum mechanics [7,8].…”