Spacing in math mode (LaTeX2e unofficial reference manual (November 2018))

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### 16.6 Spacing in math mode

When typesetting mathematics, LaTeX puts in spacing according to the normal rules for mathematics texts. If you enter `y=m x` then LaTeX ignores the space and in the output the m is next to the x, as y=mx.

But LaTeX’s rules sometimes need tweaking. For example, in an integral the tradition is to put a small extra space between the `f(x)` and the `dx`, here done with the `\,` command.

    \int_0^1 f(x)\,dx

LaTeX provides the commands that follow for use in math mode. Many of these spacing definitions are expressed in terms of the math unit mu. It is defined as 1/18em, where the em is taken from the current math symbols family (see Units of length). Thus, a `\thickspace` is something like 5/18 times the width of a ‘`M`’.

`\;`

  Synonym: `\thickspace`. Normally `5.0mu plus 5.0mu`. Math mode only.

`\:`
`\>`

  Synonym: `\medspace`. Normally `4.0mu plus 2.0mu minus 4.0mu`. Math mode only.

`\,`

  Synonym: `\thinspace`. Normally `3mu`, which is 1/6em. Can be used in both math mode and text mode (see \thinspace & \negthinspace).

  This space is widely used, for instance between the function and the infinitesimal in an integral `\int f(x)\,dx` and, if an author does this, before punctuation in a displayed equation.

      The antiderivative is
      \begin{equation}
        3x^{-1/2}+3^{1/2}\,.
      \end{equation}

`\!`

  A negative thin space. Normally `-3mu`. The `\!` command is math mode only but the `\negthinspace` command is available for text mode (see \thinspace & \negthinspace).

`\quad`

  This is 18mu, that is, 1em. This is often used for space surrounding equations or expressions, for instance for the space between two equations inside a `displaymath` environment. It is available in both text and math mode.

`\qquad`

  A length of 2 quads, that is, 36mu = 2em. It is available in both text and math mode.

Unofficial LaTeX2e reference manual