[Tex/LaTex] Set enumeration level explicitly

#enumerateenvironmentslists

I have the need for a custom list environment at the outermost level, defined as follows:

\newboolean{odd}
\setboolean{odd}{true}
\usepackage{environ}
\newcounter{exnum}[section]% Exercise counter (within section)
\NewEnviron{solution}{% Solution
   \stepcounter{exnum}%
   \ifthenelse{\isodd{\theexnum}}% Condition on oddness
      {\item \BODY}% Print odd answer
      {\ifthenelse{\boolean{odd}}{}{\item \BODY}}% Print odd
}
\newenvironment{outerlist}%
    {\begin{list}%
        {{\bfseries\arabic{exnum}.}}{}}%
    {\end{list}}%

The point of all of this is to be able to set the odd boolean and change whether all items, or just the odd-numbered items, are output.

This all works fine, except that this list environment, outerlist, does not increment the enumeration level. As a result, inner enumerations start at level 1. This is not consistent with the visual appearance (outerlist obviously looks like an outer enumeration in the output), and is confusing to the maintainer (I confused myself a couple of times 🙂

Can I tell LaTeX to start with enumeration level 2? Or is there a better way to write the above so as to get the behavior I want?

Edit: Per request, here is an MWE:

\documentclass{article}
\usepackage{environ}

\newcounter{itemnum}
\NewEnviron{outeritem}{% Solution
   \stepcounter{itemnum}%
   {\item \BODY}%
}

\newenvironment{outerlist}%
    {\begin{list}%
        {{\bfseries\arabic{itemnum}.}}{}}%
    {\end{list}}%

\renewcommand{\labelenumi}{{\bfseries(\alph{enumi})}}
\renewcommand{\labelenumii}{{\bfseries(\roman{enumii})}}

\begin{document}

\begin{outerlist}
\begin{outeritem}
  This level is numbered with arabic numerals, but is not really an enumerate list.
\end{outeritem}
\begin{outeritem}
  This is outer list item 2.
  \begin{enumerate}
    \item This looks visually to be at level 2, but LaTeX thinks of it as a level 1 enum, 
        and it is governed by $\backslash$labelenumi. I would like it to be governed by
        $\backslash$labelenumii, so that the TeX file can use level 2 definitions for 
        this list level format.
  \end{enumerate}
\end{outeritem}
\end{outerlist}
\end{document}

Best Answer

It is possible to adjust the list depth/level. Let's see what enumerate does (taken from latex.ltx):

\def\enumerate{%
  \ifnum \@enumdepth >\thr@@\@toodeep\else
    \advance\@enumdepth\@ne
    \edef\@enumctr{enum\romannumeral\the\@enumdepth}%
      \expandafter
      \list
        \csname label\@enumctr\endcsname
        {\usecounter\@enumctr\def\makelabel##1{\hss\llap{##1}}}%
  \fi}

Within the definition \advance\@enumdepth\@ne increases the depth/level of the enumeration. We could define

\newcommand{\advanceenumeratelevel}{\advance\@enumdepth\@ne}

and use it where needed:

enter image description here

\documentclass{article}
\usepackage{environ}% http://ctan.org/pkg/environ

\newcounter{itemnum}
\NewEnviron{outeritem}{% Solution
   \stepcounter{itemnum}%
   {\item \BODY}%
}
\makeatletter
\newcommand{\advanceenumeratelevel}{\advance\@enumdepth\@ne}
\makeatother

\newenvironment{outerlist}%
  {\begin{list}%
    {{\bfseries\arabic{itemnum}.}}{}}%
  {\end{list}}%

\renewcommand{\labelenumi}{{\bfseries(\alph{enumi})}}
\renewcommand{\labelenumii}{{\bfseries(\textit{\roman{enumii}})}}

\begin{document}

\begin{outerlist}
\begin{outeritem}
  This level is numbered with arabic numerals, but is not really an enumerate list.
\end{outeritem}
\begin{outeritem}
  This is outer list item 2.
  \advanceenumeratelevel
  \begin{enumerate}
    \item This looks visually to be at level 2, but LaTeX thinks of it as a level 1 enum, 
        and it is governed by $\backslash$labelenumi. I would like it to be governed by
        $\backslash$labelenumii, so that the TeX file can use level 2 definitions for 
        this list level format.
  \end{enumerate}
\end{outeritem}
\end{outerlist}
\end{document}

Since I don't know the full extent of usage for enumerate inside your lists, you may have to consider demoting the level at the end of outeritem. For example, the following may be sufficient:

\makeatletter
\newcommand{\advanceenumeratelevel}{\advance\@enumdepth\@ne}
\newcommand{\retractenumeratelevel}{\advance\@enumdepth\m@ne}
\makeatother
\newenvironment{outerlist}%
  {\advanceenumeratelevel%
   \begin{list}%
    {{\bfseries\arabic{itemnum}.}}{}}%
  {\end{list}%
   \retractenumeratelevel}%
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