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We answer the first question in Malkoun's MathOverflow 512579, revision 1: for positive semidefinite Hermitian X,Y, every elementary symmetric function of the eigenvalues of XY+YX is at most its counterpart for X^2+Y^2. The written proof establishes the stronger absolute-value inequality for arbitrary Hermitian X,Y and for H=A*B+B*A, R=A*A+B*B with arbitrary rectangular complex A,B. Cauchy-Binet and Cauchy-Schwarz bound each principal determinant, including singular cases. The pinned Lean declaration proves the original positive-semidefinite assertion; the extensions have written proofs and accompanying exact finite checks.
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Ma et al. (2026) studied this question.
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