Question: differentiation of general function

Hello people in mapleprimes

I asked a question for a similar thing before.
https://www.mapleprimes.com/questions/222751-PDEtoolsdeclare

The question I had then is not solved yet in my mind, so I think  I will ask you
again. It is about differentiation of a composite function.

with(PDEtools):
declare(f(x,y,z),g(t,y));
a:=f(x,y,z);
b:=x=g(t,y);
c:=eval(a,b);
d:=diff(c,y);
OFF;
e:=d;

h:=convert(e,diff);

For both e and d, the notation of D__1 and D__2 appear.
And, even if, with convert, I changed them to another form,
what I can get is more complicated form of h.

Is it inevitable to use D__1 and D__2 brabra in the differentiation of
composite function?

I am writing this question thinking that if there is a way of go around it,
 I want to know.

And, though this is the second question, even if I use latex( ) command,
natually, codes of Tex I can get is that of the output shown on the screen, including D__1 and D__2, even though I want it to be shown with f__x and f__y or that including prime. Then, I have to edit that tex file, changing D__1 to f__x etc. which I think is very complicated modification of the text file.
I wish there is a way to modify it in Maple so as it to be direct TeX codes which  do not require me to modify.
Is it impossible to do such a thing?

Thanks in advance.

diff_2.mw