In this paper, double commutativity and the reverse order law for the core inverse are
considered._en new characterizations of theMoore–Penrose inverse of a regular element are given
by one-sided invertibilities in a ring. Furthermore, the characterizations and representations of the
core and dual core inverses of a regular element are considered.National Natural Science Foundation of China (No.11371089). FCT project UID-MAT-00013/2013info:eu-repo/semantics/publishedVersio