# Breaking formulas before and after binary operators

Page 195 of the TeXBook reads:

Although formulas within a paragraph always break after binary operations and relations, displayed formulas always break before binary operations and relations.

What is the reason for this rule?

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(Is this question acceptable here? It's not specifically about TeX, just about math typesetting.) – Ben Alpert Jun 19 '11 at 18:30

When I write code, I break long mathematical expressions after a binary operator. That dangling operator at the end of the line gives a clue to the reader (or maintainer) that there is more to the expression at hand. When I document that code, I break before the binary operator. Think of `sum = (long expression) - (second long expression) + (third long expression) - (final long expression)`. Because of how subtraction works, pairing the operator with the subtrahend/addend as opposed to hiding the operator at the end of the previous line improves comprehensibility (at least for the sighted). – David Hammen Jun 19 '11 at 23:05