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تسجيل مستخدم جديدSemirigid systems of three equivalence relations
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A system $mathcal M$ of equivalence relations on a set $E$ is emph{semirigid} if only the identity and constant functions preserve all members of $mathcal M$. We construct semirigid systems of three equivalence relations. Our construction leads to the examples given by Zadori in 1983 and to many others and also extends to some infinite cardinalities. As a consequence, we show that on every set of at most continuum cardinality distinct from $2$ and $4$ there exists a semirigid system of three equivalence relations.
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