# How can I make three horizontal dots on a letter in plain TeX

How can I make three horizontal dots on a letter in plain TeX?

The amstex macros provide this accent.

\input amstex

$\dddot{a}$

\bye


• Well, not really: this is a very long standing bug of amstex (and amsmath). – egreg Feb 9 at 17:04
• Try $a+\dot{a}+\ddot{a}+\dddot{a}+\ddddot{a}$ – egreg Feb 9 at 17:14

You can load amstex (which is recommended if you do much mathematics), but you have to fix the definitions of \dddot (and \ddddot):

\input amstex

% fix \dddot and \ddddot
\begingroup
\catcode@=11
\gdef\dddot#1{{\mathop{\kern0pt #1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
\hbox{\rm...}\vss}}}}
\gdef\ddddot#1{{\mathop{\kern0pt #1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
\hbox{\rm....}\vss}}}}
\endgroup

$a+\dddot{a}+\ddddot{a}$

\bye


If you don't want amstex, you can use the code with some changes:

% define \dddot and \ddddot
\newdimen\ex
\ex.2326ex
\def\dddot#1{{\mathop{\kern0pt #1}\limits^{\vbox to-1.4\ex{\kern-2\ex
\hbox{\rm...}\vss}}}}
\def\ddddot#1{{\mathop{\kern0pt #1}\limits^{\vbox to-1.4\ex{\kern-2\ex
\hbox{\rm....}\vss}}}}

$a+\dddot{a}+\ddddot{a}$

\bye
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