Whether the categorical approach for determining a 'serious drug offense' under the Armed Career Criminal Act applies the federal definition of 'controlled substance' at the time of the prior state conviction, the federal offense, or federal sentencing

QUESTION PRESENTED Whether, under the categorical approach established by this Court for determining whether a previous state conviction can qualify as a predicate “serious drug offense” under the Armed Career Criminal Act (ACCA), a sentencing court is to apply the federal definition of “controlled substance” as it existed (1) at the time of the prior state conviction, (2) at the time of the commission of the federal offense, or (3) at the time of federal sentencing. i