“…We refer to the articles [40,42,43] and references therein for some recent development on the topic. In the past decade, with the establishment of difference analogues of Nevanlinna theory (see e.g., [4,8,16]), many researchers studied the solutions of Fermat type difference and also Fermat-type differential-difference equations (see [18,28,34]). Here, an equation is called differential-difference equation, if it includes derivatives, shifts or differences of f (z), which can be called DDE for short (see [31]).…”