# Widetilde and prime (derivative) position

I need to write something like {\widetilde f}' in my text, but the result looks rather ugly since the prime (derivative) sign is too low. It looks like \widetilde{f'}.

Is there any way to do this properly?

• Why not \tilde{f'}? – Sigur Jan 2 '14 at 22:16
• I'd use $\tilde{f}'$, so there wouldn't be any ambiguity about it being the derivative of “tilde f” and not ”tilde of the derivative of f”. – egreg Jan 2 '14 at 22:19
• @egreg: I just prefer \widetilde, but maybe it is indeed better to use \tilde in this case. – xen Jan 2 '14 at 22:38
• @xen You shouldn't prefer \widetilde; for lowercase letters there's no need for it (and rarely also for uppercase ones). – egreg Jan 2 '14 at 22:39
• @egreg: Oh, thanks. I didn't know that and I've got used to \widetilde. Although (maybe just for me) even with \tilde it sometimes doesn't look good to write something like \tilde{f}^n. This n "should" be over \tilde, or maybe I'm just wrong here? – xen Jan 2 '14 at 22:49

I'd avoid \widetilde, particularly above an “f”. A decoration (math accent) above a symbol is usually interpreted as a modifier of the symbol itself, so

$\tilde{f}'$


will be interpreted as “the derivative of f tilde”, rather than “tilde of the derivative of f”.

Should you feel that an ambiguity could arise, it's probably better to add parentheses

$(\tilde{f})'$


rather than raising the prime that could be mistaken for some “tilde prime”.

Below I show some examples.

As you see, raising the prime is not the answer.

• Many thanks! I just have one question. In comments you said about \widetilde: "for lowercase letters there's no need for it (and rarely also for uppercase ones)". Are there any "rules" when I should use \widetilde? – xen Jan 3 '14 at 11:46
• @xen Generally, \widetilde should be used only for decorating a group of symbols. – egreg Jan 3 '14 at 11:51