“…) and therefore compact [38], [41], [61], [63]. Thus, based on Lemma 2, Lemma 4 and on the property of compactness of F P,Q , according to a particular feature of the Fredholm Alternative Theorem ([23, Corollary 3.5], [37,Corollary 7.27]) 7 , the solution of (67) is unique and the operator T is boundedly invertible in X C and X H .…”