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  "body": "\n## Summary\n\n**Buchholz's psi-functions** are a hierarchy of single-argument ordinal functions $\\psi_\\nu(\\alpha)$ introduced by German mathematician Wilfried Buchholz in 1986. These functions are a simplified version of the $\\theta$-functions, but nevertheless have the same strength as those. Later on this approach was extended by Jäger and Schütte.\n",
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