In this paper we show how one can deduce the Titchmarsh expansion formula in eigenfunctions of Hill's operator from the Gel'fand expansion formula.
ARAS, FİLİZ and GUSEİNOV, GUSEİN SH (2001) "On the Expansions in Eigenfunctions of Hill's Operator," Turkish Journal of Mathematics: Vol. 25: No. 2, Article 7. Available at: https://journals.tubitak.gov.tr/math/vol25/iss2/7