punctuation on mathematical formulas

A standard principle for the punctuation of mathematical formulae is that they should be punctuated exactly the same as text is. Even when the formula is displayed in a separate line, it should follow standard punctuation: it should end with a dot, it should not necessarily be preceded by a colon, it should not be outside of the sentence.

Bad punctuation

Let $f:\mathbb{R}\to \mathbb{R}$ be defined by the following formula: $f(x)=e^x$ A duoidal category has a distributor $d:(X⊲W)\otimes (Y⊲Z)\to (X\otimes Y)⊲(W\otimes Z)$

Better punctuation

Let $f:\mathbb{R}\to \mathbb{R}$ be defined by $f(x)=e^x.$ A duoidal category has a distributor, $d:(X⊲W)\otimes (Y⊲Z)\to (X\otimes Y)⊲(W\otimes Z).$

As a general principle, the reader should be able to read the sentence out loud on their head, reading each mathematical symbol out loud and reaching a well-punctuated sentence.

References.

• Handbook of Writing for the Mathematical Sciences (Higham)
• Eats, Shoots, and Leaves (Truss)

Back: writing.