string: In the former (e.g, TALMUD (Moreno et al., 2012)), each pair (Y (k),Y (l)) shares a bridge that can be different from that of the other pairs; while in the latter (e.g., CDTF (Hu et al., 2013) and extended CLFM (Gao et al., 2013a)), all Y (k)’s share the same bridge.