A binary logical connective, denoted

\begin{equation*} P \iff Q \qor P \equiv Q, \end{equation*}

and read

	“\(P\) if and only if \(Q\)”
or	“\(P\) is equivalent to \(Q\)”,

that is true if and only if

\(P\) and \(Q\) are both either true or false,

which is equivalent to

\begin{equation*} (P \implies Q) \> \land \> (Q \implies P). \end{equation*}

[1, Sec. 0.2], [2, Sec. 5.1]

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