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  "body": "\n## Summary\n\nThe Herglotz–Riesz kernel of a disc is the holomorphic function of $z$ whose real part is the Poisson kernel.\nIntegrating it against the boundary values of a harmonic function $u$ gives a holomorphic function with real part $u$.\nIt is the kernel in the Schwarz integral formula and in the Herglotz representation of holomorphic functions with positive real part.\n\n## Explanations\n\n### L1 human\n\nThe Poisson kernel tells how much each boundary point of a disc counts when one rebuilds a harmonic function inside.\nThe Herglotz–Riesz kernel carries the same information, but as a holomorphic function.\nFor the unit disc and a boundary point $\\zeta$ it is $(\\zeta + z)/(\\zeta - z)$.\nAt the centre $z = 0$ it equals $1$, and it blows up as $z$ approaches $\\zeta$.\n",
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