“…Successively, Breckner, Rȃdulescu, and Varga [7] proved the existence of infinitely many solutions of problem (S f,g a,1 ) under the key assumption that the nonlinearity f is non-positive in a sequence of positive intervals (see Remark 3.2). See also the papers [2,3,4,5,6,16] and references therein for related topics.…”