http://en.wikipedia.org/wiki/Arrow%27s_impossibility_theorem
Of note, the previous summary definition of Arrow's theorem was:
"In voting systems, "Arrow's impossibility theorem", or "Arrow's paradox" demonstrates the impossibility of designing a set of rules for social decision making that would obey every "reasonable" criterion required by society."
The new summary definition on the wiki page is:
"In voting systems, "Arrow's impossibility theorem", or "Arrow's paradox" demonstrates the impossibility of designing a set of rules for social decision making that would pass all the criteria collected by Arrow in the theorem. The theorem is frequently misrepresented as a proof that a reasonable voting method is impossible."
More is added in a discussion section.
Curt
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