Formal Notation
The biconditional introduction rule may be written in sequent notation:
where is a metalogical symbol meaning that is a syntactic consequence when and are both in a proof;
or as the statement of a truth-functional tautology or theorem of propositional logic:
where, and are propositions expressed in some formal system.
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Famous quotes containing the word formal:
“Two clergymen disputing whether ordination would be valid without the imposition of both hands, the more formal one said, “Do you think the Holy Dove could fly down with only one wing?””
—Horace Walpole (1717–1797)