### Abstract

The enumeration of independent sets in graphs with various restrictions has been a topic of much interest of late. Let i(G) be the number of independent sets in a graph G and let i
_{t}(G) be the number of independent sets in G of size t. Kahn used entropy to show that if G is an r-regular bipartite graph with n vertices, then i(G) ≤ i(K
_{r,r})
^{n/2r}. Zhao used bipartite double covers to extend this bound to general r-regular graphs. Galvin proved that if G is a graph with δ(G) ≥ δ and n large enough, then i(G) ≤ i(K
_{δ,n-δ}). In this paper, we prove that if G is a bipartite graph on n vertices with δ(G) ≥ δ where n ≥ 2δ, then i
_{t}(G) ≤ i
_{t}(K
_{δ,n-δ}) when t ≥ 3. We note that this result cannot be extended to t = 2 (and is trivial for t = 0, 1). Also, we use Kahn's entropy argument and Zhao's extension to prove that if G is a graph with n vertices, δ(G) ≥ δ, and Δ(G) ≤ Δ, then i(G) ≤ i(K
_{δ;≥})
^{n/2δ}.

Original language | English |
---|---|

Journal | Electronic Journal of Combinatorics |

Volume | 19 |

Issue number | 3 |

State | Published - 27 Sep 2012 |

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## Cite this

*Electronic Journal of Combinatorics*,

*19*(3).