# 5. Extensible and adjustable symbols | LaTeX manual

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In LaTeX, there are certain features which allow producing structures that can grow to any required size. Mathematical typesetting is in dire need of such variability. We will discuss some aspects of it in this article. All commands covered in this section (unless otherwise noted) are provided by standard LaTeX.

## 5.1. Ellipsis…

The amsmath package replaces (in almost all cases) all those \ldots, cdots, etc. from standard LaTeX with the single \dots command. Both the vertical position of the ellipsis and the space around it are automatically selected depending on the type of the symbol following \dots. If the next symbol is, say, a plus sign, the dots will come out centered; if it is a comma, they will fall on the baseline. It’s always three dots but the spacing is variable.

1\usepackage{amsmath}
2% -------------------------------------------------------------------------------
3A series $H_1, H_2, \dots, H_n$, a sum
4$H_1 + H_2 + \dots + H_n$, an orthogonal product
5$H_1 \times H_2 \times \dots \times H_n$.

However, when the dots happen to appear at the end of a formula, the next object will be something like \end or \) or $, and it gives LaTeX no clue about the positioning of the dots. In such a case, you must help by using \dotsc for dots followed by commas, \dotsb for dots followed by Binary operator or Relation symbol, \dotsm for dots followed by multiplication dots, \dotsi for dots followed by integrals, or \dotso in any other case. 1\usepackage{amsmath} 2% ------------------------------------------------------------------------------- 3A series$H_1, H_2, \dotsc\,$, a sum 4$H_1 + H_2 + \dotsb\,$, an orthogonal product 5$H_1 \times H_2 \times \dotsm\,\$, and an infinite
6integral: $\int_{H_1} \int_{H_2} \dotsi \; 7{-\Gamma}\, d\Theta$

## 5.2. Symbols that are horizontally extensible

Basically, LaTeX allows setting up any math accent command to produce the appropriate glyph from a range of widths whenever these are provided by the available fonts. However, in standard LaTeX there are only two such commands: \widehat and \widetilde.

In the next example, we demonstrate the use of a few commands that produce constructs similar to the aforementioned extensible accents. They all produce compound symbols of math class Ordinary.

 1\usepackage{amsmath}
2% -------------------------------------------------------------------------------
3\begin{align*}
4\widehat {\psi_\delta(t) E_t h}
5&= \widetilde {\psi_\delta(t) E_t h} \\
6\overline {\psi_\delta(t) E_t h}
7&= \underline {\psi_\delta(t) E_t h} \\
8\overbrace {\psi_\delta(t) E_t h}
9&= \underbrace {\psi_\delta(t) E_t h}
10& & \text{Do not change style} \\
11\overrightarrow {\psi_\delta(t) E_t h}
12&= \overleftarrow {\psi_\delta(t) E_t h}