could never earn any money since the tax on revenues would always exceed the earnings. For example, grocery stores typically earn pennies on every dollar of revenue; they could not pay a tax rate of 25% on revenues unless their markup exceeded 25%. Thus, corporations must be able to deduct operating expenses even if individuals cannot. A practical dilemma arises as to identifying what is an expense for a business. For example, if a peanut butter producer purchases a jar manufacturer, is that an expense (since the producer has to purchase jars somehow) or a sheltering of income through investment? Flat tax systems can differ greatly in how they accommodate such gray areas. For example, the "9-9-9" flat tax proposal would allow businesses to deduct purchases but not labor costs, which effectively taxes labor-intensive industrial revenue at a higher rate. How deductions are implemented will dramatically change the effective total tax, and thus the flatness of the tax. Thus, a flat tax proposal is not fully defined unless the proposal includes a differentiation between deductible and non-deductible expenses. Tax effects Diminishing marginal utility Flat tax benefits higher income brackets progressively due to decline in marginal value. If a flat tax system has a large exemption, it is effectively a progressive tax. As a result, the term "flat tax" is actually a shorthand for the more proper marginally flat tax. Administration and enforcement One type of flat tax would be imposed on all income once; at the source of the income. Hall and Rabushka proposed an amendment to the U.S. Internal Revenue Code that would implement the variant of the flat tax they advocate. This amendment, only a few pages long, would replace hundreds of pages of statutory language (although most statutory language in taxation statutes is not directed at specifying graduated tax rates). As it now stands, the U.S. Internal Revenue Code is over several million words long, and contains many loopholes, deductions, and exemptions which, advocates of flat taxes claim, render the collection of taxes and the enforcement of tax law complicated and inefficient. It is further argued that current tax law slows economic growth by distorting economic incentives, and by allowing, even encouraging, tax avoidance. With a flat tax, there are fewer incentives than in the current system to create tax shelters, and to engage in other forms of tax avoidance. Flat tax critics contend that a flat