Overbrace
This command
starts a "growing" overbrace.
The cursor sets under
the overbrace symbol , so you have just to type the main part.
To finish it, type Enter as usual.
Then the cursor sets above
the overbrace
symbol, so you have just to type the over part,
for instance n times.
To finish it, and then finish the
symbol, type Enter
as usual.
The keyboard shortcut is Tab f.