Separate numberings in two equation environments

Question

I'd like to have two equation-like environments, with separate numbering, and easily use them inside various amsmath environments.

Inspired by an answer by Egreg to Clone of the `amsmath` equation environment with different spacing, I wrote

\documentclass[a4paper,10pt]{article}
\usepackage{amsmath}
\newcounter{savedequation} \newcounter{myhypo}
\newcommand{\setmyhypo}{%
   \setcounter{savedequation}{\value{equation}}%
   \setcounter{equation}{\value{myhypo}}%
   \renewcommand\theequation{$H_\arabic{equation}$}%
}
\newcommand{\unsetmyhypo}{%
   \setcounter{myhypo}{\value{equation}}%
   \setcounter{equation}{\value{savedequation}}%
}
\newenvironment{hypothesis}{%
   \setmyhypo%
   \begin{equation}%
}{%
   \end{equation}%
   \unsetmyhypo%
}
\begin{document}
\begin{hypothesis}   \label{test_1} a=b \end{hypothesis}
\begin{gather}
   \label{test_2} c=d \
   \setmyhypo
   \notag e=f \
   \label{test_3} h=i
   \unsetmyhypo 
\end{gather}
\setmyhypo 
\begin{gather}
   \label{test_4} j=k \
   \notag l=m 
\end{gather}
\unsetmyhypo
\eqref{test_1}, \eqref{test_2} and \eqref{test_4} work but not \eqref{test_3}.
\end{document}

Any idea on how to use both equation-like environments inside the same gather (it may be cleaner for alignment purpose)?

Edit: refinements:

\makeatletter
\newcommand{\setmyhypo}{%
  \setcounter{savedequation}{\value{equation}}%
  \setcounter{equation}{\value{myhypo}}%
  \renewcommand\theequation{$H_{\arabic{equation}}$}%
  \tagsleft@true\let\veqno\@@leqno%
}
\newcommand{\unsetmyhypo}{%
  \setcounter{myhypo}{\value{equation}}%
  \setcounter{equation}{\value{savedequation}}%
  \renewcommand\theequation{\arabic{equation}}%
  \tagsleft@false\let\veqno@@eqno%
}
\makeatother

PS: I still don't understand how to put automatically compiled code samples. — dominique, Oct 05 '22 at 20:18
Regarding producing output that can be posted here, this has a number of suggestions: Compile a LaTeX document into a PNG image that's as short as possible — barbara beeton, Oct 05 '22 at 20:33
@barbara: Thanks. I thought some here were able to enter code that is automatically compiled by tex.stackexchange.com online. — dominique, Oct 05 '22 at 22:23

score 0 · Accepted Answer · answered Oct 06 '22 at 07:02

Use \tag (together with code that does the necessary stuff).

I made some changes to the code, please check them.

\documentclass[a4paper,10pt]{article}
\usepackage{amsmath}
\newcounter{savedequation}
\newcounter{myhypo}
\renewcommand\themyhypo{\ensuremath{\mathrm{H}_{\arabic{myhypo}}}}
\newcommand{\setmyhypo}{%
  \setcounter{savedequation}{\value{equation}}%
  \setcounter{equation}{\value{myhypo}}%
  \renewcommand\theequation{\ensuremath{\mathrm{H}_{\arabic{equation}}}}%
}
\newcommand{\unsetmyhypo}{%
  \setcounter{myhypo}{\value{equation}}%
  \setcounter{equation}{\value{savedequation}}%
}
\newenvironment{hypothesis}{%
   \setmyhypo
   \begin{equation}%
}{%
   \end{equation}%
   \unsetmyhypo
   \ignorespacesafterend
}
\newcommand{\hypoline}{\stepcounter{myhypo}\tag{\themyhypo}}
\begin{document}
\begin{hypothesis}\label{test_1}
a=b
\end{hypothesis}
\begin{gather}
  c=d \label{test_2} \
  e=f \notag \
  h=i \hypoline \label{test_3} \
  u=v
\end{gather}
\setmyhypo 
\begin{gather}
  j=k \label{test_4} \
  l=m \notag
\end{gather}
\unsetmyhypo
\eqref{test_1}, \eqref{test_2} and \eqref{test_4} work and also does \eqref{test_3}.
\end{document}

Thanks. It is indeed cleaner. I did not use \tag initially because I also use hyperref and I was not sure it would work correctly with hyperref, but I do not see why not : I'm going to test it now. — dominique, Oct 06 '22 at 13:43
Ah, its the requirement to change the side of the tag \tagsleft@true\let\veqno\@@leqno, that I foolishly added later, that I don't see how to make work properly... It does not seem to work if called inside an amsmath environment. However it was not so important. — dominique, Oct 06 '22 at 14:04
Using your command \hypoline, there is no more real need of a specific hypothesis environment, nor of my commands \setmyhypo, \unsetmyhypo, nor of counter savedequation. — dominique, Oct 06 '22 at 14:09

Separate numberings in two equation environments

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