The Sturm--Liouville problem with singular potential and the extrema of the first eigenvalue

On the basis of the theory of Sturm–Liouville problem with distribution coefficients we get the infima and suprema of the first eigenvalue of the problem $-y\mathrm{"}+(q-\lambda )y=0,y^{\mathrm{\prime }}(0)-k_0^{2}y(0)=y^{\mathrm{\prime }}(1)+k_1^{2}y(1)=0$, where $q$ belongs to the set of constant-sign summable functions on $[0,1]$ such that ${\int }_0^{1}qdx=\pm 1$.