# Questions tagged [relation-algebra]

A relation algebra is a residuated Boolean algebra expanded with an involution called converse, a unary operation. The motivating example of a relation algebra is the set of binary relations on a set X, that is, the set of subsets of X^2.

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### Characterizing relations by forbidden induced subsets

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### Generalizing cycle/pseudo-tree factorizations for permutations/transformations to arbitrary binary relations

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### Given any finite relation $R$ what is the cardinality of $\langle R\rangle=\{\underbrace{R\circ R\cdots \circ R}_{n\text{ times}}:n\in\mathbb{N}\}$?

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### The relation on the set of functions

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### Categories with binary relations as objects

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### Why is Set, and not Rel, so ubiquitous in mathematics?

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### Why is a UNION operation independent in relational algebra?

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### Substitution semiring?

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