The minimum number of maximal independent sets in twin-free graphs

TL;DR

This paper investigates the minimum number of maximal independent sets in twin-free graphs, revealing different growth rates for arbitrary graphs, bipartite graphs, and trees, and provides new proofs for known extremal cases.

Contribution

It establishes the minimum number of maximal independent sets in twin-free graphs across various classes and offers a shorter proof for the extremal trees case.

Findings

Logarithmic minimum in arbitrary graphs

Linear minimum in bipartite graphs

Exponential minimum in trees

Abstract

The problem of determining the maximum number of maximal independent sets in certain graph classes dates back to a paper of Miller and Muller and a question of Erd\H{o}s and Moser from the 1960s. The minimum was always considered to be less interesting due to simple examples such as stars. In this paper we show that the problem becomes interesting when restricted to twin-free graphs, where no two vertices have the same open neighbourhood. We consider the question for arbitrary graphs, bipartite graphs and trees. The minimum number of maximal independent sets turns out to be logarithmic in the number of vertices for arbitrary graphs, linear for bipartite graphs and exponential for trees. In the latter case, the minimum and the extremal graphs have been determined earlier by Taletski\u{\i} and Malyshev, but we present a shorter proof.