... PR, be the corresponding real price index (deflated by the CPI), let D,, be the stock of minutes detailed by product k at the end of time period r, let Jk,, be the stock of pages of ... M, be the stock of marketing effort at the end of month t (as measured by the stocks of journal advertising and detailing minutes), let 6 be the monthly rate of de- preciation of this ... environment, let M2,1 be the marketing stock at the end of the month t that accumulated in the duopoly market environment, and let M,, be the marketing stock at the end of month t that accumulated...