What is the burden of proof when a defendant neither affirms nor denies an alleged prior conviction?

^8. We have never decided what burden of proof applies in that unusual situation (and we have found no case in which any other court has passed on the issue). In Alsol v. Mukasey, 548 F.3d 207 (2d Cir. 2008), we stated that "[i]f a defendant does not admit his prior conviction, the government must prove the existence of the prior conviction beyond a reasonable doubt." Id. at 211 (emphasis added). But that was dictum in a case that did not turn on what burden of proof applied when a defendant neither affirms nor denies an alleged prior conviction.