(28)However, in the case of ordinary debentures, because of the rights they confer on their holders, the protection of investors by means of the publication of a half-yearly report is not essential; by virtue of this Directive, convertible or exchangeable debentures and debentures with warrants may be admitted to official listing only if the related shares are already listed on the same stock exchange or on another regulated, regularly operating, recognised open market or are so admitted simultaneously; the Member States may derogate from this principle only if their competent authorities are satisfied that holders have at their disposal all the information necessary to form an opinion concerning the value of the shares to which these debentures relate; consequently, regular information needs to be coordinated only for companies whose shares are admitted to official stock-exchange listing.