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Is A = {(1,1) (1,2) (2,1)} a transitive relation on {1,2}?

It is confusing. Yes and No both seems to be right. I only need a hint.

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    You might want to explain why you think that both Yes and No are right.2012-05-27

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Hint: $(2,2)$ is not a member of $A$.

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Hint: if it were "no", you would be able to find a pair (a,b), (b,c), but you would be missing the pair (a,c).

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    You already checked `121`. Remain `111`, `112`, `212` and `211` (making 4 (not 3) more to check). When more experienced, you will see that `xxy` and `xyy` cannot be counterexamples to transitivity (can you show why?). Which would leave `121` (already checked) and `212`, and... nothing else.2012-04-30