The Nagle, et.al. textbook states: “In order to prove illegal price discrimination under the Robinson-Patman Act and assuming that the supplier sells in interstate commerce, each of five elements must

The Nagle, et.al. textbook states: “In order to prove illegal price discrimination under the Robinson-Patman Act and assuming that the supplier sells in interstate commerce, each of five elements must be present.” What are these five elements?  Does it make a difference whether the supplier is engaged in a monopoly, oligopoly or monopolistically competitive environment?  Describe the rationale for your answer.