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
Punctuation two styles differ mainly in the way in which they handle quotation marks, particularly in conjunction with other punctuation marks. In British English, punctuation such as periods and commas are placed outside the closing quotation mark; in American English, however, punctuation is placed inside the closing quotation mark. This rule varies for other punctuation marks; for example, American English follows the British English rule when it comes to semicolons, colons, question marks, and exclamation points. Other languages of Europe use much the same punctuation as English. The similarity is so strong that the few variations may confuse a native English