I'm studying Gali's work with the paper(or book?) which is "Jordi Gali, Monetary policy inflation and the business cycle_An introduction to the new keynesian framework(2015)" and wonder one thing about setting marginal cost of a firm.
On the paper chapter 3 THE BASIC KEYNESIAN MODEL, with respect to the behavioral principal of firms, he suggests an individual firm’s marginal cost in terms of the economy’s average real marginal cost as
but I cannnot understand why the first equality works since I have been teached that w/p=mpn in general.
Anybody who let me know the solution idea to solve it??
thanks in advance.