Claims

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1974_05_01_kristiansen: Kristiansen proves Erdős's conjecture for real trigonometric polynomials of degree n with 2n real roots, which gives the bound 4 of Problem 225 for all complex coefficients; the erratum the site cites concerns a companion note.

1974_11_01_saff_sheil_small: Theorem 1 of Saff and Sheil-Small gives the bound 4 for every polynomial of positive degree with all zeros on the unit circle and maximum modulus 1 there, so the display of Problem 225 holds for complex coefficients.

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