Abstract
We provide a short, elementary proof of the existence and uniqueness of the square root in the context of unbounded positive selfadjoint operators on real or complex Hilbert spaces.
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Sebestyén, Z., Tarcsay, Z. On the square root of a positive selfadjoint operator. Period Math Hung 75, 268–272 (2017). https://doi.org/10.1007/s10998-017-0192-1
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DOI: https://doi.org/10.1007/s10998-017-0192-1