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  "body": "\n## Summary\n\nA quasi-category is a [[simplicial set|WW81ARB8K9]] in which every inner horn has a filler.\nQuasi-categories are the most used model of [[(∞,1)-categories|YFY1FWA1MY]], developed by Joyal and Lurie.\nThey include both ordinary categories, through their [[nerves|RV0MKJ3CQ6]], and [[Kan complexes|FDFYCM3YYC]], which model $\\infty$-groupoids.\nMuch of ordinary category theory, including limits, adjunctions and the Yoneda lemma, extends to quasi-categories.\n\n## Explanations\n\n### L1 human\n\nA simplicial set has points, arrows between points, triangles, tetrahedra and so on.\nThink of points as objects and arrows as morphisms; a triangle with edges $f$, $g$ and $h$ says that $h$ is a composite of $f$ and $g$.\nIn a quasi-category, any two arrows that meet end to start can be composed: there is a triangle that fills them in.\nThe composite is not unique, but any two choices are linked by higher simplices, so it is unique up to a contractible space of choices.\n",
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