Basis properties of a spectral problem with spectral parameter in the boundary condition

The following boundary-value problem is considered:
\begin{gather*} y^{(4)}(x)-(q(x){y'}(x))'=\lambda y(x),\qquad 0<x<l, \\ y(0)=y'(0)=y''(l)=0, \qquad (a\lambda+b)y(l)=(c\lambda+d)Ty(l), \end{gather*}
where $\lambda$ is the spectral parameter; $Ty\equiv y'''-qy'$; $q(x)$ is a strictly positive absolutely continuous function on $[0,l]$; $a$, $b$, $c$, and $d$ are real constants such that $bc-ad>0$. The oscillation properties of eigenfunctions are studied and asymptotic formulae for eigenvalues and eigenfunctions are deduced. The basis properties in $L_p(0,l)$, $1<p<\infty$, of the system of eigenfunctions are investigated.
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