Really minor consistency nit.

Doc/lib/libobjs.tex

@@ -20,5 +20,5 @@ listing them in order of ascending priority (within a table) and
 grouping operators that have the same priority in the same box.
 Binary operators of the same priority group from left to right.
 (Unary operators group from right to left, but there you have no real
-choice.)  See Chapter 5 of the \citetitle[../ref/ref.html]{Python
+choice.)  See chapter 5 of the \citetitle[../ref/ref.html]{Python
 Reference Manual} for the complete picture on operator priorities.