摘要
Let G be a graph. An independent set Y in G is called an essential independent set (or essential set for simplicity) if there is {Y1, Y2} 包含于Y such that dist (y1,y2)=2. In this paper, we use the technique of the vertex insertion on l-connected (l=k or k+1, k≥2) graphs to provide a unified proof for G to be hamiltonian, or hamiltonian-connected. The sufficient conditions are expressed an inequality on ∑i=1 K|N(Yi)|+b|N(y0)| and n(Y) for each essential set Y={y0,y1,…,yk}, where b (1≤b≤k）is an integer,Yi={yi,yi-1,…,yi-(b-1}包含于Y\{y0} for i属于V（G):dist(v,Y)≤2}|.
