marginal
rate of substitution--- The slope at a very small interval on a
person’s utility curve
indicating the personal exchange rate
of one good for another based on the combination of these two types of things
already at hand at a particular point in space-time. This exchange
rate is quite possibly the same on another crew member’s utility curve,
and if there is perfect information in the market and the timing is right, a
door opens for trade and there is an ascent to higher utility curve/s on the
part of one or more of the “market” participants.