Stacking expressions

Formulas may become complex: we might need to put one symbol above another one or above whole expressions, or we wish to put lines, braces, or dots above symbols. There are several ways.

Underlining and overlining

\overline puts a line above its argument, which may be nested:

s = \overline{AB}

The counterpart is \underline.

It doesn't have to be a line; braces are popular too. The commands are \underbrace and \overbrace . You may use subscripts and superscripts:

N = \underbrace{1 + 1 + \cdots + 1}_n

Setting accents

We've already seen accents in text mode. For the math mode, we need different commands. They may be applied to any letter. Here's the list of math accents using the lowercase letter 'a' as an example:

The extensible ones are also called wide accents ; they try to fit the width of their argument.

Putting a symbol above another

Besides the array environment, there are amsmath commands to directly stack expressions:

• \underset{expression below}{expression} puts an expression...