“…In general, solutions of the equation do not need to exist. However, if is a nonnegative Schrödinger operator on a connected, locally finite graph, then is surjective as an operator from to [19, Theorem 2.2] (see also [5, 14]), where we have for locally finite graphs. Using the results of the previous section, we show the existence of solutions of the above equation on not necessarily locally finite graphs under the assumption of the validity of a Rellich inequality.…”