The alternative minimum tax is a tax that applies to taxpayers who otherwise would pay little or no tax because of the availability of various deductions and tax credits, I.R.C. § 55. The alternative minimum tax is an additional tax based on the difference between a tax on the taxpayer's "alternative minimum taxable income" and the tax that would otherwise be imposed, I.R.C. §§ 55(a), (b). I.R.C. §§ 56-58 describes adjustments and items of tax preference taken into account in determining alternative minimum taxable income.