Generator

Every order of arrival for three partners, and what each player adds

A generator in the applied library, called 101 times across 17 essays. Below: what it draws with nothing chosen and at each mode an essay asks for, what it checks while drawing, and everywhere it is used.

coalition is one function. Everything below came out of it during this build, at parameters taken from the essays rather than invented for this page — so a figure here is the same figure a reader meets in an essay, and if the generator changes, this page changes with it.

With nothing chosen

Every order of arrival for three partners, and what each player adds. A table with one row per order in which the players could arrive, giving what each adds to the group already present, and the average of each column as that player's share.

An exchange box, and a core that shrinks as the market grows

An exchange box, and a core that shrinks as the market grows. Edgeworth box with endowment (3,1)/(1,3), utilities xy, contract curve the diagonal; core for 1, 2, 5 replicas: 1.7321–2.2679, 1.9161–2.0839, 1.9722–2.0278.

A coalition of three that the two-trader market did not have

A coalition of three that the two-trader market did not have. Coalition of 1 A and 2 B blocks t = 2.15 at r = 2: each B gets (1.591, 2.228) worth 3.5458 > 3.4225, the A (1.817, 2.544) worth 4.6225.

Treating two traders of one kind differently invites a block

Treating two traders of one kind differently invites a block. Allocation A1 (1.9,1.9), A2 (2.1,2.1), B1 (2.1,2.1), B2 (1.9,1.9), utilities 3.61, 4.41, 4.41, 3.61; A1 and B2 block by splitting their endowments to (2,2) each, worth 4.

The core narrows to the price as the traders multiply

The core narrows to the price as the traders multiply. r = 1: 1.73205–2.26795; r = 2: 1.91608–2.08392; r = 3: 1.94987–2.05013; r = 4: 1.96424–2.03576; r = 5: 1.97220–2.02780; r = 6: 1.97726–2.02274; r = 8: 1.98333–2.01667; r = 10: 1.98684–2.01316; r = 12: 1.98913–2.01087; r = 15: 1.99138–2.00862; r = 20: 1.99359–2.00641; r = 25: 1.99490–2.00510; r = 30: 1.99576–2.00424; r = 40: 1.99684–2.00316; r = 50: 1.99747–2.00253.

The core shrinks like one over the number of traders

The core shrinks like one over the number of traders. r = 1: width 0.53590, times r 0.5359; r = 2: width 0.16784, times r 0.3357; r = 3: width 0.10025, times r 0.3008; r = 4: width 0.07152, times r 0.2861; r = 5: width 0.05560, times r 0.2780; r = 6: width 0.04548, times r 0.2729; r = 8: width 0.03334, times r 0.2667; r = 10: width 0.02632, times r 0.2632; r = 12: width 0.02174, times r 0.2609; r = 15: width 0.01724, times r 0.2586; r = 20: width 0.01282, times r 0.2564; r = 25: width 0.01020, times r 0.2551; r = 30: width 0.00847, times r 0.2542; r = 40: width 0.00633, times r 0.2532; r = 50: width 0.00505, times r 0.2525.

What it checks while it draws

Collected by running the family and recording what it asserted, not written here. The count is how many separate times the claim was put to the test while these drawings were made.

Where it is called

Every figure on this list is drawn by the same rule, so a change to the rule changes all of them at once. That is why the list is published.

Applied

A market too large to bargain in

Two traders swapping goods can settle anywhere along a stretch of possible deals; nothing forces a price. Bring in a second pair of the same traders and some of those deals can be refused by a group of three. With thirty of each, the only deals no group can refuse lie within a few thousandths of the one a price would produce. Edgeworth guessed in 1881 that competition shrinks bargaining to prices; Debreu and Scarf proved it, and the shrinking can be computed.

Applied

A share of the votes is not a share of the power

Give three members four, four and one vote, with five needed to pass. Every winning coalition needs exactly two of them, so all three have equal power — and one of them holds a ninth of the votes.

Applied

A split nobody can walk away from

Every way of dividing what a group earns is a point of a triangle, and every coalition's threat to leave cuts a straight line across it. What survives all the cuts is the set of stable divisions — and for one three-player game there is nothing left.

Applied

A vote worth nothing until it was outnumbered

From 1958 to 1973 Luxembourg held one vote of seventeen in the Council of the European Communities and could never once change an outcome. When the Council grew, Luxembourg's share of the votes fell and its share of the power rose from nothing. Power is not a quantity a member holds; it is a property of the whole assembly, and changing the assembly moves it in directions nobody would guess.

Applied

An objection one player makes to another

The core lets a coalition object to everybody at once. Narrow it to one player objecting to one other, require every such objection to be met by an equally loud one coming back, and exactly one split survives — with no dictionary order anywhere in the argument.

Applied

Cutting a link costs both of its ends the same

Three players, any two of whom can earn 1 together — but only if they are linked. Link all three and each is due a third. Remove one link and the player holding both of the others is due two thirds. Averaging over orders on the game the network allows is the one rule under which breaking any link costs the two players it joined exactly the same, and it pays go-betweens more than their links.

Applied

Each user pays for its own last link

Several users must be connected to a source, and the cheapest network that does it is a tree. Dividing its cost so that no group of users would rather build its own looks like a hard search, and it has a one-line answer: each user pays for the link that joins it to the tree on its way to the source. No group is ever overcharged — while the average over orders of arrival, the rule that settles so much else, can charge a pair more than its own connection costs.

Applied

Five weighings and the question is closed

Searching the triangle of splits can only ever fail to find a stable one, which is not the same as there being none. Weighing five families of coalitions against the whole settles the question outright — and the family that fails is the proof that nothing survives.

Applied

None of the four conditions is spare

Four conditions pick out one sharing rule. The half that is usually shown is that they are enough; the other half is that each is needed — drop any one and a different rule satisfies the rest, so the list cannot be shortened.

Applied

One glove too many

Give some people left gloves and others right ones, and let any group sell the pairs it can make. If the two sides are equal, the core — the splits no group can beat by walking out — is every price at once. If one side has a single glove more, the core is one split: the scarce side takes the whole of every pair and the other side gets nothing, however large the market. The average over orders of arrival barely notices the difference, and the two rules disagree about almost everything a market is.

Applied

Sharing a cost that is not the sum of its parts

Three users need capacities three, six and twelve of one shared thing, and serving any group costs the largest of them. Averaging what each adds over every order of arrival divides the bill — and for this family the average collapses to a rule anybody could apply by hand.

Applied

The corners are the orders of arrival

Line the players up, let each join in turn, and pay each what it adds on arrival: every order gives a split. When a newcomer always adds at least as much to a bigger group, those splits are exactly the corners of the core — so the core is never empty, it is the outline of the orders, and the average over all of them lies inside it. For a group worth the square of its size the outline is a hexagon whose corners are the six orderings of 1, 3 and 5.

Applied

The objection nobody can make louder

When no split of the winnings survives every group's objection, the core is empty and the question changes — which split makes the loudest objection as quiet as it can be? Sorting the complaints and minimising them in dictionary order picks exactly one split, always, whether or not the core exists.

Applied

The order everybody arrives in

Three people jointly earn nine, and the question is what each is owed. Ask instead what each adds on walking into a room the others are already in, average that over every order they could have arrived in, and four modest conditions leave no other answer.

Applied

Three splits that answer every other

When any two of three people can take a pound, no division of it is safe from a pair walking off. Von Neumann and Morgenstern's answer was not a division but a set of them: three half-and-half splits that never beat one another and between them beat everything else. It is a solution — and so is the line on which one player is held at any fixed share below a half, so the same game has infinitely many, each describing a different settled way of treating the third player.

Applied

Too many orders to list

The rule is an average over every order the players could have arrived in. At seven players that is five thousand orders and at twenty it is more than there are seconds in the age of the universe — so the average is sampled, and the error falls at a rate that can be measured.

Applied

What a missing input is worth

A model prices a house at 180 from its size, its garden and its bedrooms, and the question is how much of the price each input is responsible for. Make the inputs the players and the average over orders answers it — once somebody decides what the model says when an input is not known. Three reasonable decisions give bedrooms nothing, nothing, and sixteen, for a model that never reads them.

The whole library · What the figures prove