Bulk-edge correspondence is one of the most distinct properties topological insulators. In particular, 1D winding number ν has a one-to-one to edge states in chain insulators with boundaries. By properly choosing unit cells, we carry out numerical calculation show explicitly extended SSH model that numbers corresponding left and right cells may be used predict on two boundaries finite chain. Mo...

Caro, Davila, and Pepper recently proved δ(G)α(G)≤Δ(G)μ(G) for every graph G with minimum degree δ(G), maximum Δ(G), independence number α(G), matching μ(G). Answering some problems they posed, we characterize the extremal graphs δ(G)<Δ(G) as well δ(G)=Δ(G)=3.