[expr.dynamic.cast] Remove redundant statements on casting away const…

…ness

and fix the null pointer provision.

source/expressions.tex

@@ -2653,14 +2653,15 @@
 result is an xvalue of the type referred to by \tcode{T}.
 
 \pnum
-If the type of \tcode{v} is the same as \tcode{T}, or it is
-the same as \tcode{T} except that the class object type in \tcode{T} is
-more cv-qualified than the class object type in \tcode{v}, the result is
-\tcode{v} (converted if necessary).
+If the value of \tcode{v} is a null pointer value in the pointer case
+and the conditions for \tcode{T} and the type of \tcode{v} specified
+in the following paragraphs are satisfied,
+the result is the null pointer value of type \tcode{T}.
 
 \pnum
-If the value of \tcode{v} is a null pointer value in the pointer case,
-the result is the null pointer value of type \tcode{T}.
+If the type of \tcode{v} is the same as \tcode{T} (ignoring cv-qualifications),
+the result is
+\tcode{v} (converted if necessary).
 
 \pnum
 If \tcode{T} is ``pointer to \cvqual{cv1} \tcode{B}'' and \tcode{v} has
@@ -2675,8 +2676,7 @@
 \tcode{v} can contain other \tcode{B} objects as base classes, but these
 are ignored.}
 In both the pointer and
-reference cases, the program is ill-formed if \cvqual{cv2} has greater
-cv-qualification than \cvqual{cv1} or if \tcode{B} is an inaccessible or
+reference cases, the program is ill-formed if \tcode{B} is an inaccessible or
 ambiguous base class of \tcode{D}.
 \begin{example}