[iterator.requirements.general] "counted range" defines a term of art

Fixes #2931.

source/iterators.tex

@@ -614,12 +614,15 @@
 \range{i}{s} denotes a valid range.
 
 \pnum
-A counted range \range{i}{n} is empty if \tcode{n == 0}; otherwise, \range{i}{n}
-refers to the \tcode{n} elements in the data structure starting with the element
-pointed to by \tcode{i} and up to but not including the element, if any, pointed to by
-the result of \tcode{n} applications of \tcode{++i}. A counted range
-\range{i}{n} is valid if and only if \tcode{n == 0}; or \tcode{n} is positive,
-\tcode{i} is dereferenceable, and \range{++i}{-{-}n} is valid.
+A \defnadj{counted}{range} \range{i}{n} is empty if \tcode{n == 0};
+otherwise, \range{i}{n} refers to
+the \tcode{n} elements in the data structure
+starting with the element pointed to by \tcode{i} and up to but not including
+the element, if any, pointed to by
+the result of \tcode{n} applications of \tcode{++i}.
+A counted range \range{i}{n} is valid if and only if \tcode{n == 0};
+or \tcode{n} is positive, \tcode{i} is dereferenceable,
+and \range{++i}{-{-}n} is valid.
 
 \pnum
 The result of the application of library functions