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  "body": "\n## Summary\n\nA Schubert variety is a subvariety of a [[Grassmannian|CYPA882RB9]] or a [[flag variety|NHRWCQQKTH]] defined by conditions on how a subspace meets a fixed flag.\nIn a Grassmannian they are indexed by partitions that fit in a rectangle.\nTheir classes form a basis of the cohomology ring, and computing products of these classes is [[Schubert calculus|FWGHMADJR4]].\nSchubert varieties are usually singular, and their singularities are studied through combinatorics.\n\n## Explanations\n\n### L1 human\n\nFix a line $\\ell$ in three-dimensional projective space.\nThe lines that meet $\\ell$ form a three-dimensional family inside the four-dimensional space of all lines.\nThis is a Schubert variety: it is defined by one incidence condition with a fixed subspace.\nImposing stronger conditions, such as lying in a fixed plane or passing through a fixed point, gives smaller Schubert varieties.\n",
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