direct comparisons of actual prices with (HNOP + NOM) figures will rarely be practicable because of the difficulty of calculating both the HNOPs and the NOMs;
interregional and intertemporal comparisons are somewhat more practicable because it is easier to estimate acceptably accurately the relevant HNOP and NOM differences (i.
Just as oligopolistic prices are prices above a relevant seller's HNOP, predatory prices are prices below a seller's HNOP.
the factors that affect the mechanical and law-related cost of the seller's communicating the necessary anticompetitive threats and/or offers to its potential undercutters--inter alia, its reputations for estimating its HNOPs and NOMs accurately and for practicing contrived oligopolistic pricing (which affect its ability to communicate the required anticompetitive offers and/or threats cheaply, simply by charging a contrived oligopolistic price),
Sherman Act) or arranging for the relevant set of rivals to announce their prices in an order that would raise the prices in the set of their across-the-board HNOPs (and make related decisions that increase the cost they would have to incur to charge prices that deviate from their announced prices)--viz.
1] [equivalent to] the best-placed seller's overall marginal cost if he charges the relevant buyer his HNOP.
2] [equivalent to] the contextual marginal costs the second-placed seller would have to incur to match or infinitesimally beat the bestplaced seller's HNOP offer.
2] [equivalent to] the overall marginal costs the second-placed seller would have to incur to match or infinitesimally beat the best-placed seller's HNOP offer.
Not represented: the contextual marginal costs and hence overall marginal cost that the best-placed seller would have to incur to make a sale or even an offer at a price that exceeded his HNOP or the contextual marginal and hence overall marginal cost that a second-placed seller would have to incur to match or infinitesimally beat any offer by a best-placed seller that contained a price that exceeded the latter's HNOP