If a mathematical word begins with a number and a hyphen, such as "4-dimensional" or $3-manifold," and this word occurs at the beginning of a sentence, should you capitalize the first letter?
For example, which is correct?
3-dimensional space is nice.
or
3-Dimensional space is nice.
The convention in mathematical writing is to never begin a sentence with a mathematical symbol, so as to avoid this ambiguity. Instead of writing, "$5$-dimensional manifolds have the disjoint disks property," or "$5$-Dimensional manifolds have the disjoint disks property," I would write "Five dimensional manifolds have the disjoint disks property." This removes all ambiguity. Instead of writing "$f$ is a continuous function," I would write "The function $f$ is continuous."
Though I have no personal experience in professional editing, I am told that editors in general (meaning even outside of mathematics and science) find ways to reword sentences to avoid the ambiguities that arise frequently in English, and, I assume, other languages.