Can a defendant be convicted of making a false declaration if one of the declarations is irreconcilably contradictory?

Under 18 U.S.C. Sec. 1623(a), the government must prove the falsehood of a declaration beyond a reasonable doubt in order to obtain a conviction. In contrast, the "inconsistent declarations" subsection provides that a defendant may be convicted of making a false declaration if he or she has made two irreconcilably contradictory declarations such that one of them is necessarily false. 18 U.S.C. Sec. 1623(c). It is not necessary for the government to prove which of the two contradictory declarations is false. 18 U.S.C. Sec. 1623(c); see also Dunn v. United States, 442 U.S. 100, 108, 99 S.Ct. 2190, 2195, 60 L.Ed.2d 743 (1979).