In mathematics, the transitive closure of a binary relation R on a set X is the transitive relation R+ on set X such that R+ contains R and R+ is minimal (Lidl and Pilz 1998:337). If the binary relation itself is transitive, then the transitive closure is that same binary relation; otherwise, the transitive closure is a different relation. For example, if X is a set of airports and x R y means "there is a direct flight from airport x to airport y", then the transitive closure of R on X is the relation R+: "it is possible to fly from x to y in one or more flights."
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