Much of the controversy surrounding the claims of Holocaust deniers centers on the methods used to present arguments that the Holocaust allegedly "never happened as commonly accepted". Numerous accounts have been given by Holocaust deniers (including evidence presented in court cases) of claimed facts and evidence; however, independent research has shown these claims to be based upon flawed research, biassed statements, or even deliberately falsified evidence. Opponents of Holocaust denial have documented numerous instances in which such evidence was altered or manufactured (see Nizkor Project and David Irving). According to Pierre Vidal-Naquet, "in our society of image and spectacle, extermination on paper leads to extermination in reality."