In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then G is isomorph...In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then G is isomorphic to M if and only if the set of the orders of the maximal abelian subgoups of G is the same as that of M .展开更多
A graph G is k-triangular if each of its edge is contained in at least k triangles. It is conjectured that every 4-edge-connected triangular graph admits a nowhere-zero 3-flow. A triangle-path in a graph G is a sequen...A graph G is k-triangular if each of its edge is contained in at least k triangles. It is conjectured that every 4-edge-connected triangular graph admits a nowhere-zero 3-flow. A triangle-path in a graph G is a sequence of distinct triangles T1T2%…Tk in G such that for 1 〈 i 〈 k - 1, IE(Ti)∩E(Ti+1)1= 1 and E(Ti) n E(Tj)=φ if j 〉 i+1. Two edges e, e'∈ E(G) are triangularly connected if there is a triangle-path T1, T2,... , Tk in G such that e ∈ E(T1) and er ∈ E(Tk). Two edges e, e' ∈E(G) are equivalent if they are the same, parallel or triangularly connected. It is easy to see that this is an equivalent relation. Each equivalent class is called a triangularly connected component. In this paper, we prove that every 4-edge-connected triangular graph G is Z3-connected, unless it has a triangularly connected component which is not Z3-connected but admits a nowhere-zero 3-flow.展开更多
In this paper, we prove that if any set of |E(G)|- |V(G)| + 1 facial cycles of a 3-connected planar graph G embedded in the plane doesn't form a minimum cycle base of G, then any minimum cycle base of G cont...In this paper, we prove that if any set of |E(G)|- |V(G)| + 1 facial cycles of a 3-connected planar graph G embedded in the plane doesn't form a minimum cycle base of G, then any minimum cycle base of G contains a separating cycle, and G has a minor isomorphic to T6, where T6 is the graph obtained from the complete graph K6 by deleting a path with four edges.展开更多
The base graph of a simple matroid M=(E,A)is the graph G such that V(G)=A and E(G)={BB':B,B'B,[B/B'|=1},where the same notation is used for the vertices of G and the bases of M.It is proved that the base g...The base graph of a simple matroid M=(E,A)is the graph G such that V(G)=A and E(G)={BB':B,B'B,[B/B'|=1},where the same notation is used for the vertices of G and the bases of M.It is proved that the base graph G of connected simple matroid M is Z3-connected if|V(G)|≥5.We also proved that if M is not a connected simple matroid,then the base graph G of M does not admit a nowhere-zero 3-flow if and only if IV(G)[=4.Furthermore,if for every connected component Ei(i≥2)of M,the matroid base graph Gi of Mi=MIEi has IV(Gi)|≥5,then G is Z3-connected which also implies that G admits nowhere-zero 3-flow immediately.展开更多
Suppose that G is a planar cubic graph withχi(G)>5.We show that ifχi(H)<χi(G)for each planar cubic graph H of order less thanG,thenG is either a 3-connected simple planar cubic graph,or a planar graph obtaine...Suppose that G is a planar cubic graph withχi(G)>5.We show that ifχi(H)<χi(G)for each planar cubic graph H of order less thanG,thenG is either a 3-connected simple planar cubic graph,or a planar graph obtained from a simple cubic 3-connected planar graph by adding some earrings.This shows that a minimum non-5-injectively colorable simple planar cubic graph must be 3-connected.展开更多
摘要In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then G is isomorphic to M if and only if the set of the orders of the maximal abelian subgoups of G is the same as that of M .
摘要A graph G is k-triangular if each of its edge is contained in at least k triangles. It is conjectured that every 4-edge-connected triangular graph admits a nowhere-zero 3-flow. A triangle-path in a graph G is a sequence of distinct triangles T1T2%…Tk in G such that for 1 〈 i 〈 k - 1, IE(Ti)∩E(Ti+1)1= 1 and E(Ti) n E(Tj)=φ if j 〉 i+1. Two edges e, e'∈ E(G) are triangularly connected if there is a triangle-path T1, T2,... , Tk in G such that e ∈ E(T1) and er ∈ E(Tk). Two edges e, e' ∈E(G) are equivalent if they are the same, parallel or triangularly connected. It is easy to see that this is an equivalent relation. Each equivalent class is called a triangularly connected component. In this paper, we prove that every 4-edge-connected triangular graph G is Z3-connected, unless it has a triangularly connected component which is not Z3-connected but admits a nowhere-zero 3-flow.
摘要In this paper, we prove that if any set of |E(G)|- |V(G)| + 1 facial cycles of a 3-connected planar graph G embedded in the plane doesn't form a minimum cycle base of G, then any minimum cycle base of G contains a separating cycle, and G has a minor isomorphic to T6, where T6 is the graph obtained from the complete graph K6 by deleting a path with four edges.
基金supported in part by the National Natural Science Acknowledgements Foundation of China(Grant No.61700230).
摘要The base graph of a simple matroid M=(E,A)is the graph G such that V(G)=A and E(G)={BB':B,B'B,[B/B'|=1},where the same notation is used for the vertices of G and the bases of M.It is proved that the base graph G of connected simple matroid M is Z3-connected if|V(G)|≥5.We also proved that if M is not a connected simple matroid,then the base graph G of M does not admit a nowhere-zero 3-flow if and only if IV(G)[=4.Furthermore,if for every connected component Ei(i≥2)of M,the matroid base graph Gi of Mi=MIEi has IV(Gi)|≥5,then G is Z3-connected which also implies that G admits nowhere-zero 3-flow immediately.
基金This research was supported by the National Natural Science Foundation of China(Nos.11571180 and 11331003)the Natural Science Foundation of Jiangsu Higher Education Institutions of China(No.17KJB110010).
摘要Suppose that G is a planar cubic graph withχi(G)>5.We show that ifχi(H)<χi(G)for each planar cubic graph H of order less thanG,thenG is either a 3-connected simple planar cubic graph,or a planar graph obtained from a simple cubic 3-connected planar graph by adding some earrings.This shows that a minimum non-5-injectively colorable simple planar cubic graph must be 3-connected.