Differences Between Theorems Modules (AMS and non AMS)

[Udicoudco]

Hello Lyx Developers,

Recently I've been trying to understand more thoroughly how theorems
modules are implemented in LyX, and I think I've come across some bugs, and
some redundant modules (but I might have misunderstood a few things).

The first thing I've noticed is that all AMS theorems related modules load
the packages amsmath and amsthm even if the use did not use any layout.  I
could not understand why, as amsthm does not depend on amsmath.  I've tried
to compile a lyx file containing all the layouts defined in Theorem (AMS),
but i erased the line "Require amsmath,amsthm" from the module, and the
file compiled (as amsthm is loaded by the layouts, there is no really a
need to load the package if the user did not use any layout).

The second thing I've noticed, there is no difference between the files
theorems.inc and theorems-ams.inc. In the description of the file
theorems-std.module, which uses theorems.inc it is said that the module
"Defines some theorem environments for use with non-AMS classes", but the
module uses amsthm, and he is compilable with AMS classes.

The only difference I've found between theorems.inc and theorems-ams.inc,
is the list of layouts the files provide at the beginning of the files (but
they provide the same layouts, with the exact same definitions. I've used
text comparison software to verify that).

Because of that, I've concluded that the only differences between
theorems-std.module and theorems-ams.module is that in theorems-std.module
there are no unnumbered theorems (as theorems-ams.module  includes
theorems-starred.inc, but theorems-std.module  does not),
theorems-std.module does not load amsmath, and loads amsthm only if the
user has used a layout that is not the proof layout, and the definition of
the proof layout.

I did not understand the purpose of the file theorems-proof-std.inc. This
file is included in theorems-std.module, and it appears that this file is
defining the proof environment (but the definition is quite different from
the usual one), if it is not defined. Since amsthm defines the proof
environment,  if i will compile a file using Theorems module, the
appearance of my proofs will depend if i used another  layout provided by
the module. Wont it be more reasonable to add to the proof layout defined
in theorems-proof.inc the line "Require amsthm" and use this layout? if
there is a theorems module that does not use amsthm (and currently i don't
think there is one like that), it could include  theorems-proof-std.inc.

Another problem with the fact that the proof layout in theorems-proof.inc
does not require amsthm, is with the module Theorems (Unnumbered). This
module only loads amsthm if the user use one of the theorems layouts. if
one would simply use the proof layout with this module, and no other layout
from the module, with non-AMS class (as these classes also defines the
proof environment), he will get the error "LaTeX Error: Environment proof
undefined.".

Another inquiry I have about the module Theorems (Unnumbered) is the file
theorems-starred-equivalents.inc. This file only copies the starred
theorems layouts but gives the new layout a name without a star, e.g., it
defines a Theorem layout exactly as Theorem* layout (and this files misses
the Fact layout).

For all these reasons i believe that with a little bi of modification to
the non AMS modules (which actually use amsthm), the AMS modules are
redundent, and it is probably wise to add the line "Require amsthm" to the
proof layout.

If this suggestion seems reasonable to everybody, i could start work on the
matter, and send the relevent files after editing them as mentioned.

Just for clerification, all the modules files i've mentioned are the ones
that comes with LyX2.3.6.1.

Best Regards,
Udi
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