In People v. Earls (1992) 10 Cal.App.4th 184, the defendant's opening brief revealed that he based his appeal on noncertificate grounds, but his notice of appeal did not state that his appeal was based on such grounds. ( Id. at p. 191.) In dismissing the defendant's appeal, this court stated, "over 18 months have passed since the date of filing and the defendants and their counsel have not attempted to amend the notice of appeal or sought other relief. The purpose of section 1237.5 and, by reasonable inference, its implementing rule of court, is to discourage and weed out frivolous or vexatious appeals following guilty pleas. When a defendant fails to satisfy the requirements of that section and rule and the record discloses no justification for that failure, the appeal is not operative and the appropriate disposition is dismissal." ( Id. at p. 193.)