Use the calc package to ignore \baselinestretch around case labels.

diff --git a/mjo-proof_by_cases.tex b/mjo-proof_by_cases.tex
index f2d9b90987c8b894d74f8f38c41b16a620931029..daf08a8ec22006892de0b4a81d2d2a365ef8c3a2 100644 (file)
--- a/mjo-proof_by_cases.tex
+++ b/mjo-proof_by_cases.tex
@@ -12,6 +12,27 @@
 % Used below to define pcases.
 \usepackage{enumitem}
 
+% Needed to perform division in the definition of \singleblskip.
+\usepackage{calc}
+
+% A \baselineskip without the \baselinestretch scaling factor. Even
+% though \baselinestretch defaults to 1.0, it doesn't really have that
+% value. Thus to avoid division by zero, we need to do the ``is this
+% thing empty?'' hack.
+%
+% If we use \baselineskip instead of \singleblskip in our list, things
+% get real ugly when the text is e.g. double-spaced.
+%
+\newlength{\singleblskip}
+\setlength{\singleblskip}{
+  \baselineskip / \real{
+      \if\relax\detokenize{\baselinestretch}\relax
+        \baselinestretch%
+      \else
+        1%
+      \fi}
+}
+
 % Using the enumitem package, we define a new type of list, called
 % ``pcases'' (proof by cases). Each case has a label with an arabic
 % numeral (the case number), but also a \thiscase identifier. The
@@ -26,7 +47,7 @@
   leftmargin=0pt,
   listparindent=\parindent,
   parsep=\parskip,
-  itemsep=\baselineskip}
+  itemsep=\singleblskip}
 
 % The optional argument here gets stuffed into the \thiscase macro, to
 % be called by pcases when it creates this list item. The \hfill is a
@@ -35,5 +56,5 @@
 % so we consume the rest of the line instead.
 \newcommand{\case}[1][]{
   \def\thiscase{#1}%
-  \item \hfill\par\vspace{\baselineskip}
+  \item \hfill\par\vspace{\singleblskip}
 }