What is the burden of proof at the penalty phase?

As the Attorney General observes, the jury was instructed that the prosecution must prove defendant's other crimes or prior felony convictions beyond a reasonable doubt, and that to return a death verdict, each juror must be persuaded "that the aggravating circumstances are so substantial in comparison with the mitigating circumstances that it warrants death instead of life without parole." We have repeatedly rejected the argument that the federal or state Constitution, or Evidence Code sections 115 and 500, require further instructions on the subject of the burden of proof at the penalty phase. (See People v. Welch, supra, 20 Cal.4th at pp. 767-768, 85 Cal.Rptr.2d 203, 976 P.2d 754; People v. Holt, supra, 15 Cal.4th at pp. 682-684, 63 Cal.Rptr.2d 782, 937 P.2d 213.)