Yes, Speiser's theorem is an if and only if.

See Theorem 1 and "Corollary to Theorem 1" in Levinson and Montgomery's Zeros of the derivatives of the Riemann Zeta-function. Acta Math. 133 (1974), 49–65.

Yes, Speiser's theorem is an if and only if.

See Theorem 1 and "Corollary to Theorem 1" in Levinson and Montgomery's Zeros of the derivatives of the Riemann Zeta-function. Acta Math. 133 (1974), 49–65.

Edit: An English language explication of Speiser's proof can be found in Arias-de-Reyna's X-ray of Riemann Zeta Function

Yes, Speiser's theorem is an if and only if.

See Theorem 1 and "Corollary to Theorem 1" in Levinson and Montgomery's Zeros of the derivatives of the Riemann Zeta-function. Acta Math. 133 (1974), 49–65.

Yes, Speiser's theorem is an if and only if.

See Theorem 1 and "Corollary to Theorem 1" in Levinson and Montgomery's Zeros of the derivatives of the Riemann Zeta-function. Acta Math. 133 (1974), 49–65.