Best and recommended way to write prime on i in $i^{th}$

Question

I have two $i^{th}$ and $i^{\prime th}$ and it is hard to see prime in $i^{\prime th}$. I would like to know the opinion of expert LaTeX users about this. I wonder what is the best and recommend way to write $i^{th}$ and $i^{\prime th}$.

Answer 1

The superscript "th" seems to have come into use in the Victorian age; then it was dropped and it resurrected when some word processor made it their default. See the nice column on TUGboat by Peter Flynn about this (TUGboat 26, n. 3, 2005, p.~196).

In mathematical writing such a use can be confused with exponents: what does

$i^{th}$

mean? Is it "i raised to the power th" or an ordinal?

So I believe it is best to use

$i$-th

where the hyphen is clearly not a minus and so this construction is semantically sound. In case of the $i'$-th element one might think whether expanding it into the element at place~$i'$ is better.