“…In part, the missing hypothesis in Example 2.3 of [18] and in Example 1 at the end of Section 2 of [12] as well as the lack of any proof have been the motivation for writing this paper, and especially, for proving the simplicity criterion Theorem 2.3. Moreover, as far as I can see, most of the existing papers on (semi-)simple Leibniz algebras (for example, [18], [12], [4], [5], [2]) do not use a conceptual approach, and the latter is exactly what we will present here. In particular, in Section 2 we discuss how our results can be employed to prove some of the statements in previous papers on (semi-)simple Leibniz algebras or sometimes how to complete the proofs of these statements.…”