Nash equilibrium

A pair of choices where neither player gains by changing their choice alone. There can be several, or none in pure actions.

Dominant strategy

A choice that does better against every possible choice of the other player. A weakly dominant choice can tie against some choices.

Pareto efficiency

An outcome where improving one player’s payoff requires making the other worse off. This does not measure fairness or effects on outsiders.

A model and an experiment

The payoff table describes a single encounter. A simulation shows what particular strategies do over repeated encounters. Repetition changes the larger game, even when the single-encounter table stays the same.

Utility points

These are illustrative preferences, not a forecast or measured money. Comparing or adding different people’s utility requires assumptions. Randomized calculations assume the numbers represent cardinal utility.