Where the words come from
Oligopolists' mutual interdependence and the choice between competing and colluding; product differentiation through advertising, brand names, quality and services; advertising making demand less elastic or shifting it — Principles of Economics 2e, OpenStax, licensed CC BY 4.0. https://openstax.org/books/principles-economics-2e/pages/10-2-oligopoly and https://openstax.org/books/principles-economics-2e/pages/10-1-monopolistic-competition. Changes: 10.2's "If oligopolists compete hard, they may end up acting very much like perfect competitors, driving down costs and leading to zero profits for all" condensed; the point that non-price advantages are slower to copy is ours; 10.1's intangible aspects ("a reputation for high quality, services like free delivery") used for the quality card; the ketchup blindfold example and the advertising card (perceived demand more inelastic, or shifted right) condensed from 10.1, with Pigou's point that rival campaigns neutralise each other given as the cola example; the loyalty scheme card, the broadband and loyalty card examples and the price war sentence are ours; the recap's limit pricing clause summarises this page's own block; British spelling.
The question and the page layout are our own.