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  "body": "\n## Summary\n\nA semiring of sets is a family of sets that contains the empty set and is closed under intersections of two members.\nIn it, the difference of two members is a finite disjoint union of members.\nThe half-open intervals of the real line form the main example.\nMeasures such as Lebesgue measure are often first defined on a semiring and then extended.\n\n## Explanations\n\n### L1 human\n\nA semiring of sets is a family of simple building blocks.\nTwo blocks overlap in a block, and cutting one block out of another leaves finitely many separate blocks.\nHalf-open intervals $[a, b)$ are the picture to keep in mind: $[0, 3) \\setminus [1, 2)$ is the two blocks $[0, 1)$ and $[2, 3)$.\nLength is easy to define on such blocks, and measure theory extends it to much more complicated sets.\n",
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