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Latex symbol if and only if / equivalence

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How to write if and only if symbol / equivalence in Latex ? In mathematics, if and only if (iff) is a biconditional logical connective between statements, where either both statements are true or both are false.

How to write if and only if symbol / equivalence in Latex ?

You do not have to use any package:

A $\Leftrightarrow$ B \\
C $\Longleftrightarrow$ D

For a short if and only if, use \Leftrightarrow:
A $\Leftrightarrow$ B

For a long if and only if, use \Longleftrightarrow:
C $\Longleftrightarrow$ D

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