The lower independence number i(G) of a graph G is the minimum size of a maximal independent vertex set in G. The lower indepedence number is equiavlent to the "independent domination number" (i.e., the minimum size of an independent dominating set; cf. Crevals and Östergård 2015) since the lower independence number gives the minimum size of a maximal independent vertex set but any maximal independent set is minimal dominating. The (upper) independence number may be similarly defined as the largest size of an independent vertex set in G .