In economics, lexicographic preferences or lexicographic orderings describe comparative preferences where an agent prefers any amount of one good (X) to any amount of another (Y). Specifically, if offered several bundles of goods, the agent will choose the bundle that offers the most X, no matter how much Y there is. Only when there is a tie between bundles with regard to the number of units of X will the agent start comparing the number of units of Y across bundles. Lexicographic preferences extend utility theory analogously to the way that nonstandard infinitesimals extend the real numbers. With lexicographic preferences, the utility of certain goods is infinitesimal in comparison to others. Etymology Lexicography refers to the compilation of dictionaries, and is meant to invoke the fact that a dictionary is organized alphabetically: with infinite attention to the first letter of each word, and only in the event of ties with attention to the second letter of each word, etc. Example As an example, if for a given bundle (X;Y;Z) an agent orders his preferences according to the rule X>>Y>>Z, then the bundles {(5;3;3), (5;1;6), (3,5,3)} would be ordered, from most to least preferred: 5;3;3 5;1;6 3;5;3 Even though the first option contains fewer total goods than the second option, it is preferred because it has more Y. Note that the number of X's is the same, and so the agent is comparing Y's. Even though the third option has the same total goods as the first option, the first option is still preferred because it has more X. Even though the third option has far more Y than the second option, the second option is still preferred because it has more X. Discontinuity A lexicographic preference relation is not a continuous relation. This is because, for a decreasing convergent sequence we have , while the limit (0,0) is smaller than (0,1). Utility function representation A distinctive feature of such lexicographic preferences is that a multivariate real domain of an agent's preferences does not map into a real-valued range. That is, there is no real-valued representation of a preference relation by a utility function, whether continuous or not. Lexicographic preferences are the classical example of rational preferences that are not representable by a utility function. Proof: suppose by contradiction that there exists a utility function U representing lexicographic preferences, e.g. over two goods. Then U(x,1)>U(x,0) must hold, so the intervals [U(x,0),U(x,1)]