The problem is to find some signal or clue or rationalization that both can perceive as the "right" one, with each party prepared to be disciplined by that signal or clue in the event that it appears to discriminate against him. They must find their clues where they can. (If the map they are using happens, for example, to contain an embarrassing richness of clues, making it difficult to single out any particular one, a fairly arbitrary line drawn as a suggestion by the referee, identical on both maps, might have to be accepted as a "mediator," even if it is substantially biased toward one of the players.)

Thomas C. Schelling, The Strategy of Conflict, loc. 236