What is the test for invalidating a death sentence for a violent criminal with five prior convictions?

Defendant asks this court to invalidate his death sentence on the ground that it was not proportional to his moral culpability. We disagree. Defendant, a career criminal with five prior felony convictions, brutally beat to death an aged, defenseless man so he could rob the victim of his meager possessions. On these facts, the death sentence is not "grossly disproportionate to the defendant's individual culpability" (People v. Dillon (1983) 34 Cal.3d 441, 479, 194 Cal.Rptr. 390, 668 P.2d 697), nor is it "`disproportionate to the defendant's "personal responsibility and moral guilt"'" (People v. Marshall (1990) 50 Cal.3d 907, 938, 269 Cal.Rptr. 269, 790 P.2d 676).

Defendant contends the aggravating circumstances in section 190.3, as communicated to the jury through the trial court's instructions, are unconstitutionally vague as applied because they failed to guide and limit the jury's discretion so as to avoid an arbitrary and capricious application of the death penalty. He notes that the jury was allowed to double-count the restaurant robbery both as violent criminal conduct ( 190.3, factor (b)) and as a prior felony conviction ( 190.3, factor (c)). He acknowledges that in People v. Melton, supra, 44 Cal.3d 713, 764-765, 244 Cal.Rptr. 867, 750 P.2d 741, we held that the jury may engage in such double-counting, but he points out that here the jury was not told of the constitutional principles that led us to uphold such double-counting. He offers no explanation as to why the jury must be instructed on these principles, and we perceive none.