Market Structure & Price Equilibrium

Abstractions about how markets clear and firms set prices under different competitive structures — classifying goods by rivalry and excludability, computing consumer/producer surplus, and modeling monopoly, oligopoly, and auction-like price competition (Bertrand, Cournot, Hotelling) toward or away from efficient equilibrium.

25 abstractions in this family — domain-specific abstractions that sit near one another in structural-signature space (k-means over structural-signature embeddings). Each is shown with its short description.

• Arrow–Debreu Model — Prove that a competitive economy has a set of prices at which every market clears at once, by treating each date-and-state-indexed good as its own priced commodity and applying a fixed-point argument to joint excess demand.
• Bertrand Paradox (Economics) — Compute the extreme corner of price competition — two firms selling an identical good at equal marginal cost price at marginal cost with zero profit — as a deliberately-wrong baseline whose gap to real margins becomes a five-assumption diagnostic audit.
• Bundling — A seller conditions access to one good on accepting another by offering a combined package, extracting more surplus when component valuations are dispersed and negatively correlated — or leveraging market power in one good to foreclose rivals in a complementary one.
• Channel Conflict — The distribution failure mode in which a producer's new direct pathway to customers undercuts the margins its own intermediaries depend on, triggering rational retaliation that erodes the expected gain — so a new channel's true worth is gross gain minus incumbent-channel loss.
• Club Good — Classify a shared resource as excludable-and-non-rival-up-to-congestion, which fixes that it can be provided privately by membership fee, and select its pricing regime by which side of the congestion threshold it sits on.
• Coase Theorem — State that with clear property rights and zero transaction costs, parties bargain to the same efficient allocation whatever the initial assignment — so the assignment fixes only who pays whom, and observed inefficiency is read contrapositively as the signature of a specific friction.
• Cobweb Model — The economic model of self-sustaining price-quantity oscillation in markets with a rigid production lag, where producers commit output on today's price and discover it clears at another — tracing a cobweb spiral whose stability follows from the supply-to-demand slope ratio.
• Common-Pool Resource — The taxonomy cell for a good that is rival yet non-excludable — a conjunction that opens an appropriability gap between private and social cost, switching on the overuse dynamic and posing a three-way governance choice: privatize, regulate, or self-govern.
• Consumer Surplus — The aggregate welfare buyers gain by paying a market price below what each would have been willing to pay, measured as the area between the demand curve and the price line — giving voluntary exchange's buyer-side value a monetary magnitude for welfare analysis.
• Demand Shaping — The supply-chain practice of applying pricing, promotion, substitution, and channel levers to the consumer side of a capacity mismatch — moving realized demand toward feasible supply rather than scaling supply to meet it — by steering the marginal consumer's selection.
• Double Marginalization — Explain why a chain of firms each holding pricing power ends up charging more and selling less than a single integrated firm would, because each node adds its markup while ignoring the demand-shrinking externality that markup imposes on the other node's profit base.
• Edgeworth Paradox — Show that Bertrand's price-equals-marginal-cost result collapses once firms face capacity constraints below total demand: no pure-strategy equilibrium exists and prices cycle endlessly between the competitive floor and monopoly ceiling.
• Excludability — Classify a good by whether non-payers can feasibly be kept from consuming it, and cross that with rivalry to place it in the four-cell Samuelsonian map — private, club, common-pool, public — each cell carrying its own provision pathology and remedy.
• Gross Domestic Product — Compress a whole economy's heterogeneous output into one scalar by summing the market value of final goods and services produced within a geographic boundary over a fixed period, cross-checked by three coincident production, expenditure, and income identities.
• Hotelling's Law — The result that two share-maximizing suppliers competing for uniformly distributed consumers who patronize the nearest provider converge on minimum differentiation — both clustering at the median — a share-maximizing yet welfare-minimizing equilibrium whose predictions shift in signed directions as its base-case assumptions are relaxed.
• Lerner index — Collapse a firm's market power into one dimensionless number, the markup of price over marginal cost as a fraction of price, L = (P − MC) / P, which under profit maximization also equals the reciprocal of the demand elasticity the firm faces.
• Market power — Gauge an actor's ability to profitably set price above (or wages below) the competitive level by reading the slope of the downward-sloping residual demand curve it faces, quantified as the price-cost wedge (P − MC)/P.
• Maverick Spend — Read off-contract buying not as indiscipline but as rational channel selection — local units declining a coordination tax that exceeds the central channel's marginal value — so the lever is closing the friction differential, not policing, and enforcement-only pushes spend further underground.
• Monopolistic Competition — A market structure where many small firms each sell a differentiated product — giving each a downward-sloping demand curve and local pricing power — while free entry erodes any profit until price equals average cost, leaving excess capacity as the standing signature.
• Monopsony power — Gauge a buyer's ability to set the price it pays below the competitive level by the slope of the upward-sloping residual supply curve it faces (finite elasticity ε), which yields a markdown of roughly 1/ε and the double distortion of underpayment plus under-hiring.
• Oligopoly — A market structure of a few sellers each large enough that its choices visibly move the others, so optimal strategy turns on anticipating rivals' responses — with the outcome swinging between competitive and monopoly-leaning by which equilibrium template (Cournot, Bertrand, Stackelberg, or repeated-game collusion) the market fits.
• Partial Equilibrium — The Marshallian method of isolating one market and solving its equilibrium price and quantity off supply and demand while holding the rest of the economy as fixed background — trading economy-wide feedbacks for tractability, valid only when the studied market is small and weakly connected.
• Producer Surplus — The gap between the price a seller receives and its reservation price (marginal cost), aggregated as the area between the market price line and the supply curve — the seller's side of a conserved welfare ledger that any market distortion redistributes or destroys.
• Social Surplus — Measure a market's total net benefit as the area between the demand and supply curves — consumer plus producer surplus — so a policy's efficiency cost reads off the deadweight-loss triangle of trades the price wedge suppresses, distinct from surplus merely transferred.
• Supply — Model producer behavior as a whole price-to-quantity schedule rather than a single quantity, upward-sloping because expanding output raises marginal cost, so any disturbance either moves output along the curve (only the good's own price) or shifts the whole curve (everything else).