mailing-list for TeXmacs Users

[Joris van der Hoeven <address@hidden>]

On Thu, 22 May 2003, Forringer, Ted wrote:

> > You may type "d space y" for "d applied to y". In fact,
> > you rather *should* type "d tab tab space y". Indeed,
> > the upright "d" stands for the differentiation operator.
>
> Thanks for the response, but I am afraid I still cannot get what I need.
>
> "d <space> y" does give something that looks OK, and it would be
> appropriate for the top of the differential because the differential
> operator 'd/dx' is applied to 'y'. But for the 'dx' on the bottom 'd' is
> not being applied to 'x' but the whole thing is part of one operator
> 'd/dx' so 'd <space> x' looks wrong to me.

Semantically speaking, I do not agree with you. If you write "dy/dx",
then I read "the quotient between the differentials dy and dx",
which exists if y is a function of x (check Leibniz or Newton).
Even if you consider "d/dx" as an operator, then it really is
the operator which associates "dy/dx" to "y".

> Also, it may be a cultural difference, but every math and physics
> textbook I have in my office uses a italic 'd' in the differentials, not
> an upright one, so using the 'd<tab>' is not going to help me.  (On my
> system 'd<tab><tab>' gives the partial differential which is also not
> what I am looking for.)

People took a bad habit of using the italic d, because it is more
natural to obtain with TeX/LaTeX. Nevertheless, many editors do
prefer authors to make a distinction between the operator d and
the letter d. This is best done by using a special character
for differentiation, even though you might display it in
an italic fashion. This has also been foreseen in Unicode by the way.

> Maybe I am wrong, that is OK with me, I am just wondering 'can it be
> done?'  Can I have two letters in a row in math mode where both letters
> are italics and there is no extra space between them?

Yes; it suffices to insert a dummy expression like an empty group.
But I am afraid that this is not what you should do here.