This was first discussed at [1].

In this context, "efficient" means "on the efficient frontier," while "inefficient" means "not on the efficient frontier." The construction of efficient shopping lists involves the construction of two efficient frontiers. One represents efficiency from an individual consumer's point of view. The other represents an information-aware point of view. It is assumed that the individual consumer wants the maximum bang (or other desirable quantity, and/or the minimum amount of undesirable quantities) for the minimum buck (price). This minimization and maximization stuff constitutes the maxhi schema. It is assumed that an informational cooperative wants opportunities to fill in informational gaps in its database, and take (vicariously, by way of its volunteers) "field trips" to sites that are underrepresented in the database. The movement frontier therefore reflects a preference for items about which little or nothing is known over items the database knows much about. Likewise, for vendors about which the database knows little. Shopping with a shopping list that is movement-efficient is a way in which one can contribute consumer surplus to the common store of knowledge.