My prime symbol is not superscript

Question

I'm learning math mode and having an issue here with the prime symbol.

$y\in[0,1]^{d\prime}$

In this inline math formula, the prime symbol is supposed to be superscript, but it shows up at the regular text level and size.

Answer 1

It is not clear what you want the output to be

$y\in[0,1]^{d\prime}$

the \prime is in the superscript along with d. If you want the prime to be on d then just use

$y\in[0,1]^{d'}$

which is equivalent to

$y\in[0,1]^{d^{\prime}}$

Answer 2

\prime is by default on the same level as normal text. (Just as \circ - used as symbol for degrees for example.) Instead you need to specify that \prime is a superscript:

$y\in[0,1]^{d^\prime}$

EDIT: This might be marginal to the question, but I think it's a useful addition. The ' is a shorthand for ^\prime. Thus, if you type in LaTeX:

$y\in[0,1]^{d^{\circ'}}$

the output will be:

As you can see, LaTeX interprets it as a double superscript. Now suppose you don't want that, but instead something like:

If you try to do it by typing: $y\in[0,1]^{d^{\circ}'}$, you'll summon up an error:

! Double superscript.
<recently read> ^
l.4 $y\in[0,1]^{d^{\circ}'

To avoid this, \prime comes handy. Just do: $y\in[0,1]^{d^{\circ\prime}}$ and everything will be fine. :)