  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 $-y" + (q-\lambda) y=0, y'(0) -k_0^2 y(0) = y'(1) + k_1^2 y(1) = 0$,
where $q$ belongs to the set of constant-sign summable functions on $[0,1]$
such that $\int_0^1 q dx=\pm 1$.
