Federal mandatory minimum sentencing statutes limit the discretion of a sentencing court to impose a sentence that does not include a term of imprisonment or the death penalty. They have a long history and come in several varieties: the not-less-than, the flat sentence, and piggyback versions. Federal courts may refrain from imposing an otherwise required statutory mandatory minimum sentence when requested by the prosecution on the basis of substantial assistance toward the prosecution of others. First-time, low-level, non-violent offenders may be able to avoid the mandatory minimums under the Controlled Substances Acts, if they are completely forthcoming. The most common imposed federal mandatory minimum sentences arise under the Controlled Substance and Controlled Substance Import and Export Acts, the provisions punishing the presence of a firearm in connection with a crime of violence or drug trafficking offense, the Armed Career Criminal Act, various sex crimes include child pornography, and aggravated identity theft. Critics argue that mandatory minimums undermine the rationale and operation of the federal sentencing guidelines which are designed to eliminate unwarranted sentencing disparity. Counter arguments suggest that the guidelines themselves operate to undermine individual sentencing discretion and that the ills attributed to other mandatory minimums are more appropriately assigned to prosecutorial discretion or other sources. State and federal mandatory minimums have come under constitutional attack on several grounds over the years, and have generally survived. The Eighth Amendment's cruel and unusual punishments clause does bar mandatory capital punishment, and apparently bans any term of imprisonment that is grossly disproportionate to the seriousness of the crime for which it is imposed. The Supreme Court, however, has declined to overturn sentences imposed under the California three strikes law and challenged as cruel and unusual. Double jeopardy, ex post facto, due process, separation of powers, and equal protection challenges have been generally unavailing. The United States Sentencing Commission's Mandatory Minimum Penalties in the Federal Criminal Justice System (2011) recommends consideration of amendments to several of the statutes under which federal mandatory minimum sentences are most often imposed.