Mustafin, M. A. On the Riesz basis of a sine system. (Russian) Zbl 0696.34013 Differ. Uravn. 25, No. 10, 1832-1833 (1989). Let \(0<x_ 0<1\), \(x_ 0\neq (1-2m+2s)/(1+2m+2s)\) for \(m=1,2,...\), \(s=0,1,2,... \). The author proves that the eigenfunction system \(\{\sin \pi kx/(1+(-1)^{k+1}x_ 0)\}^{\infty}_{k=1}\) of the nonlocal boundary value problem \(u''+\lambda u=0\), \(u(0)=0\), \(u(1)=u(x_ 0)\) is a Riesz basis in \(L^ 2[0,1]\). Reviewer: N.Bozhinov MSC: 34B10 Nonlocal and multipoint boundary value problems for ordinary differential equations 42C30 Completeness of sets of functions in nontrigonometric harmonic analysis 42C15 General harmonic expansions, frames Keywords:second order differential equation; eigenfunction system; nonlocal boundary value problem; Riesz basis PDFBibTeX XMLCite \textit{M. A. Mustafin}, Differ. Uravn. 25, No. 10, 1832--1833 (1989; Zbl 0696.34013)