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In [[propositional calculus|propositional logic]], '''biconditional introduction'''<ref>Hurley</ref><ref>Moore and Parker</ref><ref>Copi and Cohen</ref> is a [[validity|valid]] [[rule of inference]]. It allows for one to [[inference|infer]] a [[Logical biconditional|biconditional]] from two [[Material conditional|conditional statements]]. The rule makes it possible to introduce a biconditional statement into a [[formal proof|logical proof]]. If <math>P \to Q</math> is true, and if <math>Q \to P</math> is true, then one may infer that <math>P \leftrightarrow Q</math> is true. For example, from the statements "if I'm breathing, then I'm alive" and "if I'm alive, then I'm breathing", it can be inferred that "I'm breathing [[if and only if]] I'm alive". Biconditional introduction is the [[Converse (logic)|converse]] of [[biconditional elimination]]. The rule can be stated formally as:
:<math>\frac{P \to Q, Q \to P}{\therefore P \leftrightarrow Q}</math>
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