79As a preliminary point, the requirement of legal certainty, on which economic operators are entitled to rely, entails that when there is a dispute concerning the existence of an infringement of competition law the Commission, which bears the burden of proving infringements which it finds, must adduce evidence which will sufficiently establish the existence of the facts constituting the infringement. With specific regard to the alleged duration of an infringement, the same principle of legal certainty requires that, if there is no evidence directly establishing the duration of an infringement, the Commission should adduce at least evidence of facts sufficiently proximate in time for it to be reasonable to accept that that infringement continued uninterruptedly between two specific dates.