What is the prosecution's burden of proof in a criminal case?

The prosecution has the burden "to prove beyond a reasonable doubt those alleged prior convictions challenged by a defendant." (In re Yurko (1974) 10 Cal.3d 857, 862.) We apply a substantial evidence standard of review in evaluating a challenge to a trial court's finding that the defendant incurred a prior strike or prior serious felony conviction. (See People v. Delgado (2008) 43 Cal.4th 1059, 1067.) "In reviewing the sufficiency of the evidence of the prior convictions, we determine '". . . whether a reasonable trier of fact could have found that the prosecution sustained its burden of proof beyond a reasonable doubt. In making this determination, [we] must consider the evidence in a light most favorable to the judgment and presume the existence of every fact the trier could reasonably deduce from the evidence in support of the judgment.'"" (People v. Jones (1995) 37 Cal.App.4th 1312, 1315.)