How do I make a \therefore in *plain tex* ?

[Philip Taylor (Hellenic Institute)]

On 30/04/2023 04:16, Steve Litt wrote:
> Thanks Yuri,
>
> Your \input amssym solution works almost perfectly. The one downside is
> that the dot triangle's size doesn't change with the math font size,
> using either your \input fontch method or Philip's \scaled \magstep2
> method. The size of the dot triangle is always the same.
>
> The font that controls the \therefore must be something other than what
> Philip had on his list of enlarged fonts.
>
> Does anybody know how to make the \therefore symbol from the amssym
> package grow and shrink with the math font?
\input amssym

$ \therefore $

\font \tenmsa = msam10 scaled \magstep 2
\font \sevenmsa = msam7 scaled \magstep 2
\font \fivemsa = msam5 scaled \magstep 2

\textfont \msafam = \tenmsa
\scriptfont \msafam = \sevenmsa
\scriptscriptfont \msafam = \fivemsa

\font \tenmsb = msbm10 scaled \magstep 2
\font \sevenmsb = msbm7 scaled \magstep 2
\font \fivemsb = msbm5 scaled \magstep 2

\textfont \msbfam = \tenmsb
\scriptfont \msbfam = \sevenmsb
\scriptscriptfont \msbfam = \fivemsb

$\therefore$

\end

-- 
/Philip Taylor/

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