Your authors present several different views of the social impact of advertising. Informational advertising is thought to permanently increase demand and therefore to be productive. Persuasive or business stealing advertising is thought to be wasteful, as the expenditures do not increase overall demand, but merely transfer demand from one product to another. A third point of view is that advertising can be used to create barriers to entry, thus deterring competition. Explain how this third phenomenon may work - in other words, how might advertising act a deterrent to entry?