[iterator.operations] Simplify distance requirements; change to expects

Author: CaseyCarter

source/iterators.tex

@@ -2592,6 +2592,13 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\expects
+\tcode{last} is reachable from \tcode{first}, or
+\tcode{InputIterator} meets
+the \oldconcept{RandomAccessIterator} requirements and
+\tcode{first} is reachable from \tcode{last}.
+
 \pnum
 \effects
 If \tcode{InputIterator} meets the \oldconcept{RandomAccessIterator} requirements,
@@ -2600,15 +2607,6 @@
 \tcode{first}
 to
 \tcode{last}.
-
-\pnum
-\requires
-If \tcode{InputIterator} meets the \oldconcept{RandomAccessIterator} requirements,
-\tcode{last} shall be reachable from \tcode{first} or \tcode{first} shall be
-reachable from \tcode{last}; otherwise,
-\tcode{last}
-shall be reachable from
-\tcode{first}.
 \end{itemdescr}
 
 \indexlibrary{\idxcode{next}}%