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单词 ExampleOfAntisymmetric
释义

example of antisymmetric


The axioms of a partial ordering demonstrate that every partial ordering is antisymmetric. That is: the relationMathworldPlanetmath on a set S forces

ab and ba implies a=b

for every a,bS.

For a concrete example consider the natural numbersMathworldPlanetmath ={0,1,2,} (as defined by the Peano postulates (http://planetmath.org/PeanoArithmetic)). Take the relation set to be:

R={(a,a+n):a,n}×.

Then we denote ab if (a,b)R. That is, 57 because (5,7)=(5,5+2) and both 5,2.

We can prove this relation is antisymmetric as follows: Suppose ab andba for some a,b. Then there exist n,msuch that a+n=b and b+m=a. Therefore

b=a+n=b+m+n

so by the cancellation property of the natural numbers, 0=m+n. But by the first piano postulateMathworldPlanetmath, 0 has no predecessor, meaning 0m+n unless m=n=0.

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更新时间:2025/5/4 21:36:23