function! MyFoldLevel(lnum)
    let cur_line = getline(a:lnum)

    " Fold sections at level 1
    if cur_line =~ '^\s*\\section'
        return '>1'
    endif

    " Fold subsections at level 2
    if cur_line =~ '^\s*\\subsection'
        return '>2'
    endif

    " Fold subsubsections at level 3
    if cur_line =~ '^\s*\\subsubsection'
        return '>3'
    endif

    " Fold following environments
    let fold_envs = ['figure', 'algorithm', 'frame']
    let envs = '\(' . join(fold_envs, '\|') . '\)'

    if cur_line =~ '^\s*\\begin{' . envs
        return 'a1'
    endif

    if cur_line =~ '^\s*\\end{' . envs
        return 's1'
    endif

    return '='
endfunction