sentences:  Second, Congress usually uses the words at the beginning of subsection (a), "subject to subsection (b)," and at the beginning of subsection (b), "notwithstanding subsection (a) of this section," to define heightened penalty provisions, not separate crimes.Finally, forcing the government to prove at trial that the defendant had previously been convicted of a crime risks making trials inherently unfair insofar as the jury, faced with such evidence, would be more inclined to convict the defendant on the basis of those prior convictions alone rather than the evidence that he is guilty of the presently charged crime.The recidivism exception to the Sixth Amendment.