Look at table 236 in the Comprehensive LaTeX Symbol List that you can find using the question linked as duplicate.
– egregApr 15 '22 at 08:52
@egreg \ddot{r} works thanks. But I do not understand your sentence: that you can find using the question linked as duplicate as I'm not a native speaker; could you reword it ?
– user2925716Apr 15 '22 at 11:48
\ddot{r}? – egreg Apr 15 '22 at 08:13\ddot{r}works thanks. But I do not understand your sentence:that you can find using the question linked as duplicateas I'm not a native speaker; could you reword it ? – user2925716 Apr 15 '22 at 11:48