Alternative numbering for AMS "Theorem" environment

Question

I am currently writing a LyX document using the extended AMS package. My document consists of theorems of two types. So far, I used the standard Theorem environment (the one with numbering) for the theorems of the first kind, and the Theorem* environment (no numbering) for theorems of the second kind, to emphasize the difference between the two.

Nevertheless, this is problematic when I want to include cross references to theorems of the second kind, since they do not have numbering attached to them. If I do label them and put a cross reference, then they are automatically assigned a number, which only appears in the cross reference (and not in the theorem itself), which also makes no sense.

While I still want to keep these theorems looking different than the first type theorems, I do want to be able to cross reference to them. I thought about maybe giving them different numbering - Theorem 1, 2, 3 instead of numbering according to section + order (which is the style used for the theorems of the first type). But such numbering is not an option in the extended AMS package I am using.

Does anyone have an idea on what to do about this? Either a way to create theorems with alternative numbering, or some other clever way to keep these theorems somewhat different than the standard numbered theorems, while still being able to cross reference to them.

Thanks in advance!

Answer 1

I ended up adapting the suggestion by egreg. I added the following to the LyX local layout section in the document settings:

Style Bigtheorem
CopyStyle             Theorem
DependsOn               Theorem
LatexName             bigthm
LabelString           "Theorem."
Preamble
  \usepackage{etoolbox}
  \theoremstyle{plain}
  \newtheorem{bigthm}{\protect\bigthmname}
  \makeatletter
  \makeatother
EndPreamble
LangPreamble
  \providecommand{\bigthmname}{_(Theorem)}
EndLangPreamble
BabelPreamble
  \addto\captions$$lang{\renewcommand{\bigthmname}{\Alph(Theorem)}}
EndBabelPreamble

end

This gives a new type of theorem, which is numbered individually.