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The Oxford style guide rules say this about abbreviating ranges of numbers and page references:

For a span of numbers generally, use an en rule, eliding to the fewest number of figures possible: 30–1, 42–3, 132–6, 1841–5. But in each hundred do not elide digits in the group 10 to 19, as these represent single rather than compound numbers: 10–12, 15–19, 114–18, 214–15, 310–11.

How do I implement this for a range of pages or another dynamic range of numbers in TeX/LuaTeX?

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\documentclass{article}
\usepackage{fontspec} % for easy UTF-8 support -- change en-dashes to '--' below to get rid of this dependency

\usepackage{luacode}
\usepackage{xifthen}
\usepackage{refcount}

\usepackage{lipsum} % used only for the test pages in this document

\begin{luacode}
function common_prefix(a, b)
  for idx = 1, string.len(a) do
    if a:sub(idx, idx) ~= b:sub(idx, idx) then
      return a:sub(1, idx - 1)
    end
  end
end

function numberrange_string(a, b)
  as = tostring(a)
  bs = tostring(b)
  if a == b then
    return as
  elseif as:len() ~= bs:len() then
    return as .. "–" .. bs
  else
    common_range = common_prefix(as, bs)
    if common_range:len() == 0 then
      return as .. "–" .. bs
    elseif as:sub(as:len() - 1, as:len() - 1) == "1" then
      return common_range:sub(1, common_range:len() - 1) .. as:sub(common_range:len(), as:len()) .. "–" .. bs:sub(common_range:len(), bs:len())
    else
      return common_range:sub(1, common_range:len()) .. as:sub(common_range:len() + 1, as:len()) .. "–" .. bs:sub(common_range:len() + 1, bs:len())    
    end
  end
end

function numberrange(a, b)
  tex.print(numberrange_string(a, b))
end
\end{luacode}

\newcommand{\numberrange}[2]{\directlua{numberrange(#1, #2)}}
\newcommand{\pagerefrange}[2]{\ifthenelse{\equal{\getpagerefnumber{#1}}{\getpagerefnumber{#2}}}%
  {p.~\pageref{#1}}%
  {pp.~\numberrange{\getpagerefnumber{#1}}{\getpagerefnumber{#2}}}}

\begin{document}
Some simple number ranges: \numberrange{1}{2}, \numberrange{21}{24}, \numberrange{97}{156}, \numberrange{109}{112}, \numberrange{112}{115}, \numberrange{151}{158}, \numberrange{1100}{1113}, \numberrange{11564}{11615}, \numberrange{12991}{13001}*.

Some page ranges: Test 1: \pagerefrange{test1-start}{test1-end}; Test 2: \pagerefrange{test2-start}{test2-end}; Test 3: \pagerefrange{test3-start}{test3-end}; Test 4: \pagerefrange{test4-start}{test4-end}; Test 5: \pagerefrange{test5-start}{test5-end}.

\clearpage
Test 1 is all on the same page. \label{test1-start}\label{test1-end}

Test 2 starts on the same page as Test 1, but ends on a different one. \label{test2-start}

Test 5 also starts here. \label{test5-start}

\clearpage
This is the end of Test 2. \label{test2-end}

\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]

\clearpage
Test 3 shows how ranges in the teens don’t get elided. \label{test3-start}

\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]

\clearpage
Test 3 ends here. \label{test3-end}

\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]
\clearpage \lipsum[1]

\clearpage
Test 4 shows how ranges in the twenties to nineties do get elided. \label{test4-start}

\clearpage \lipsum[1]
\clearpage \lipsum[1]

\clearpage
Test 4 ends here. \label{test4-end}

Test 5 also ends here. It shows how ranges where the ends have different numbers of digits are written in full. \label{test5-end}

\end{document}

I got a list of test cases from Peter Kahrel’s page and confirmed that this passes all of them.

N.B. I happen to disagree with Kahrel’s test case and interpretation of the rules concerning the treatment of ranges spanning teen-thousands: where he has ‘12991–3001’, I would have 12991–13001, on the grounds that one would say ‘twelve thousand nine hundred and ninety-one to thirteen thousand and one’ and not ‘… to three thousand and one’. Since I don’t personally have to deal with ranges this large, the code above does not handle them.

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