Reply To: Vector in a fraction
All of this is easier to visualize if we have a picture of the print example plus simbraille to look at. I will do my best with the print representation you have included.
d sub f - d sub o/t sub f - t sub o
[braille]?_;d;f"-_;d;o"/t;f"-t;o"#
Delta d/Delta t
[braille]?_.,d_;d/.,dt#
The typeform (bold) for a letter must always be followed by an alphabetic indicator (if the letter is Greek, this would be the Greek letter indicator). You do not also need an English letter indicator when the letter is other than English.
The typeform rule says that boldface type must be preserved when identifying letters as vectors. It is not necessary to also indicate the subscripts as boldface.