Displaying within the margins

Table of Contents

Typesetting TeXniques - This article is part of a series.

Part 5: This Article

In the series Typesetting TeXniques, we share our expertise as professional copyeditors and typesetters of mathematics. We frequently hear from authors that our work makes their papers better. This is how we do it.

Displayed math is often too wide to fit within the margins of a page without the addition of line breaks. Choosing these breaks judiciously is an element of good typesetting. Thoughtful horizontal positioning of the resulting lines is another. The simple set of principles here serves as a guide for typesetting equations, inequalities, and the like when they require multiple lines.

Choosing line breaks
#

Principle L1. If possible, keep displayed “equations” to one line:

$$ \lbrace\textrm{short and sweet}\rbrace\subset\lbrace\textrm{short}\rbrace\subset\lbrace\textrm{on one line}\rbrace $$

Principle L2. If you must add breaks, the best places to do so are at top-level relational operators (=, <, and so on).

Alignments and other horizontal positioning
#

Principle H1. When there are two or more top-level relational operators where you should break, align at those points:

$$ \begin{align*} \textrm{something} &<\textrm{something more} \cr &\ll \textrm{more more more more more more more more more more more more more} \end{align*} $$

Principle H2. When there is only one top-level relational operator and you’re breaking across lines there, push the first line to the left margin and the second to the right.

Principle H3. When you are forced to add breaks in positions other than at top-level relational operators, push the first and last lines to the margins and “staircase” any lines between:

A three-line display with no logical alignment point — Staircasing.

Examples
#

In the first video accompanying this post, an MSP production editor applies Principles L2 and H2 as part of improving this display:

A two-line display with no logical alignment point — A wide equation with one top-level relational operator (“before”).

In the second video, the production editor improves this display:

A multiple-line display with a bad alignment — A multiple-line display with an inappropriate alignment (“before”).

Because the expression between the first and second equals signs of the display is wider than the page, it’s not possible to avoid breaking that expression across lines. But the alignment in the second line is inappropriate (a set of alignment points should reflect some parallelism in the math).

In the video, the production editor removes the alignment from the second line and instead follows Principle H3. Additionally, a change to the code ensures that the outermost parentheses in the first and second lines of the display agree in size.