“…For a discussion about the existence of infinitely many solutions for differential equations, using Ricceri's Variational Principle [30] and its variants ( [7] and [27]), we refer the reader to the papers [3,4,8,9,10,11,13,14,15,18,19,21,25,31]. We also refer the reader to the papers [26,28,29] where the existence of infinitely many solutions for some boundary value problems has been studied by using different approaches.…”