1. What is a competitive market — many firms, identical product, free entry/exit; each firm is a price taker
2. Revenue of a competitive firm — TR = P × Q; AR = P; MR = P
3. Profit maximisation — produce where MR = MC (i.e. P = MC)
4. Short-run shutdown — shut down (Q = 0) if P < AVC; ignore sunk fixed costs
5. Sunk costs — already committed; irrelevant to the produce-today decision (“spilt milk”)
6. Long-run exit / entry — exit if P < ATC; enter if economic profit > 0
7. Measuring profit on the graph — profit = (P − ATC) × Q (rectangle)
8. Short-run market supply — horizontal sum of firms’ MC curves above AVC (N fixed)
9. Long-run market supply — entry/exit drives economic profit to zero; P = min ATC
10. Why stay at zero profit — zero economic profit still covers opportunity costs (normal return)
11. Demand shifts — short run: price moves more; long run: entry/exit adjusts quantity
12. Why LR supply may slope up — limited inputs or higher-cost entrants

One-line goal:

Use MR = MC to choose output, P vs AVC to decide shutdown, and P vs ATC to decide exit — and see how entry and exit build the long-run supply curve.