Letter (paper size) "official" "Government Letter" size, , was used in government, while paper was standard in most other offices. In the U.S., paper density is usually measured in "pounds per ream" (of 500 sheets). Typical Letter paper has a basis weight of paper of – the weight of 500 sheets (a ream) of paper at and at 50% humidity. One ream of 20-pound Letter-sized paper weighs , and a single Letter-sized sheet of 20-pound paper weighs , which is equivalent to 75.19 g/m. Some metric information is typically included on American ream packaging. For example, 20-pound paper is also labeled as 75
Many-one reduction in: We say that a class C of languages (or a subset of the power set of the natural numbers) is "closed under many-one reducibility" if there exists no reduction from a language in C to a language outside C. If a class is closed under many-one reducibility, then many-one reduction can be used to show that a problem is in C by reducing a problem in C to it. Many-one reductions are valuable because most well-studied complexity classes are closed under some type of many-one reducibility, including P, NP, L, NL, co-NP, PSPACE, EXP, and many others. These classes