摘要
For a graph G, we denote by c（G） the circumference of G, and let σ<sub>3</sub>（G）=min{sum from i=1 to 3 d（v<sub>i</sub>）:{v<sub>1</sub>, v<sub>2</sub>, v<sub>3</sub>} is an independent set in G},<sub>3</sub>（G）=min{sum from i=1 to 3 d（v<sub>i</sub>）-|N（v<sub>i</sub>）|:{v<sub>1</sub>, v<sub>2</sub>, v<sub>3</sub>} is an independent set in G}, ρ<sub>3</sub>（G）=min{|N（v<sub>i</sub>）|:{v<sub>1</sub>, v<sub>2</sub>, v<sub>3</sub>} is an independent set in G}
