Vertex criticality for upper domination and irredundance

Let π be any of the domination parameters ir γ, i, β, Γ or IR. The graph G is π‐critical (π⁺‐critical) if the removal of any vertex of G causes π(G) to decrease (increase). We show that the classes of IR‐critical and Γ‐critical graphs coincide, and exhibit a class of Γ⁺‐critical graphs. © 2001 John Wiley & Sons, Inc. J Graph Theory 37: 205–212, 2001