The LaTeX command for iff (⟺) is \iff (if and only if (wide)).
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| Command | Package | Use it when |
|---|---|---|
\iff recommended | none | "If and only if": a long double arrow with extra space on both sides. Built into LaTeX. |
\Leftrightarrow | none | Shorter double arrow, common inside formulas. |
\Longleftrightarrow | none | Same arrow as \iff, without the added spacing. |
\text{iff} | amsmath | The abbreviation spelled out. |
Write \iff inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. It is part of core LaTeX math, so no extra package is required.
$x^2 = 1 \iff x = \pm 1$Open this example in the live preview: it renders as you type, with no compiler and no signup.
\Leftrightarrow (⇔): if and only if\implies (⟹): implies (wide)\Rightarrow (⇒): implies\to\leftarrow\rightarrow\leftrightarrow\Leftarrow\Rightarrow\Leftrightarrow\implies\uparrow\downarrow\updownarrow\nearrow\searrow\swarrowArrows in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \iff in math mode; it needs no extra package. For example, $x^2 = 1 \iff x = \pm 1$.
None: \iff is built into LaTeX, so no extra package is required.
\iff needs no package: it is defined in LaTeX itself as \;\Longleftrightarrow\;, which is why it looks wider than \Longleftrightarrow.