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  "body": "\n## Summary\n\nA relation algebra is a [[Boolean algebra|0XADJKM699]] with two more operations and a constant.\nThey behave like [[composition|0PYSR20HGF]] and [[converse|054K3HNN5Z]] of [[binary relations|05AVARPXA2]] and like the identity relation.\nAlfred Tarski gave the axioms in the 1940s, building on the calculus of relations of De Morgan, Peirce and Schröder.\nThe main example is the algebra of all binary relations on a set.\nRelation algebras give an algebraic form of a fragment of first-order logic.\nTarski and Givant showed that set theory can be formalized in this setting.\n\n## Explanations\n\n### L1 human\n\nRelations such as \"is a parent of\" can be combined in several ways.\nComposing \"parent of\" with itself gives \"grandparent of\", and taking its converse gives \"child of\".\nThey also form a Boolean algebra: one can take \"parent or sibling\", \"not a parent\", and so on.\nA relation algebra keeps the laws that these operations obey and studies them abstractly, without a set of people in the background.\n",
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