[cpp.subst] Reword paragraph to simplify the logical structure and avoid ambiguous references.

Author: tkoeppe

source/preprocessor.tex

@@ -743,23 +743,24 @@
 \pnum
 After the arguments for the invocation of a function-like macro have
 been identified, argument substitution takes place.
-A parameter in the replacement list --- unless it is
-\mname{VA_OPT}\tcode{(}\placeholder{content}\tcode{)}, preceded by a
-\tcode{\#}
-or
-\tcode{\#\#}
-preprocessing token, or followed by a
-\tcode{\#\#}
-preprocessing token (see below) ---
-is replaced by the corresponding argument after all macros
-contained therein have been expanded, in which case,
-each argument's preprocessing tokens are completely
-macro replaced before being substituted as if they formed the rest of the
-preprocessing file with
-no other preprocessing tokens being available.
-The replacement for \mname{VA_OPT}\tcode{(}\placeholder{content}\tcode{)}, unless preceded by a
-\tcode{\#} or \tcode{\#\#} preprocessing token or followed by a \tcode{\#\#}
-preprocessing token, is the preprocessing token sequence for the corresponding argument.
+For each parameter in the replacement list that is neither
+preceded by a \tcode{\#} or \tcode{\#\#} preprocessing token nor
+followed by a \tcode{\#\#} preprocessing token, the preprocessing tokens
+naming the parameter are replaced by a token sequence determined as follows:
+\begin{itemize}
+\item
+  If the parameter is of the form
+  \mname{VA_OPT}\tcode{(}\placeholder{content}\tcode{)},
+  the replacement preprocessing tokens are the
+  preprocessing token sequence for the corresponding argument.
+\item
+  Otherwise, the replacement preprocessing tokens are the
+  preprocessing tokens of corresponding argument after all
+  macros contained therein have been expanded. The argument's
+  preprocessing tokens are completely macro replaced before
+  being substituted as if they formed the rest of the preprocessing
+  file with no other preprocessing tokens being available.
+\end{itemize}
 \begin{example}
 \begin{codeblock}
 #define LPAREN() (