In long-run competitive equilibrium, P = MC = SRATC = LRATC. Because P = MR, we can write the preceding condition as P = MR = MC = SRATC = LRATC. The condition thus consists of four parts:
(a) P = MR,
(b) MR = MC,
(c) P = SRATC,
(d) SRATC = LRATC.
Part (b)—MR = MC—is true because the perfectly competitive firm attempts to maximize profits, and that equation represents how it does so. What are the explanations for (a), (c), and (d)?