Structural rule A famous structural rule is known as cut. Considerable effort is spent by proof theorists in showing that cut rules are superfluous in various logics. More precisely, what is shown is that cut is only (in a sense) a tool for abbreviating proofs, and does not add to the theorems that can be proved. The successful 'removal' of cut rules, known as "cut elimination", is directly related to the philosophy of "computation as normalization" (see Curry–Howard correspondence); it often gives a good indication of the complexity of deciding a given logic. Structural rule In proof theory, a structural rule is
Two-man rule Two-man rule The two-man rule, also known as the four-eyes principle, is a control mechanism designed to achieve a high level of security for especially critical material or operations. Under this rule all access and actions require the presence of two authorized people at all times. Per US Air Force Instruction (AFI) 91-104, "the two-person concept" is designed to prevent accidental or malicious launch of nuclear weapons by a single individual. In the case of Minuteman missile launch crews, once a launch order is received, both operators must agree that it is valid by comparing the authorization code in the