On the characteristic values of linear integral equations

on the basis of the general analytic properties of the kernel K (x, ~) such as im tegrability, continuity, differentiability, analyticity and the like? The l i tera ture where this and analogous questions are t rea ted is v e r y considerable [HELLI~G~n-To~eLITZ, I]. ~ A relatively small par t of this l i terature, however, has points of contact with the present paper, the discussion of the majori ty of papers published on the subject being based on various special properties of the kernels. I t is assumed frequent ly tha t the kernel belongs to some special class of functions, or tha t it coincides with the Green 's funct ion of a different ial or integro-differential boundary value problem. Problems of this sort will be excluded f rom the scope of our paper a l though they are in teres t ing f rom a theoret ical point of view and impor tan t for the applications.