Fix circular dependency between null equality and identity.

docs/language/dartLangSpec.tex

 \documentclass{article}
 \usepackage{epsfig}
 \usepackage{color}
 \usepackage{dart}
 \usepackage{bnf}
 \usepackage{hyperref}
 \usepackage{lmodern}
 \newcommand{\code}[1]{{\sf #1}}
 \title{Dart Programming Language  Specification \\
 {\large Version 1.9}}
@@ skipping 4271 matching lines @@
  
 \LMHash{}
 An {\em equality expression} is either a relational expression (\ref{relationalExpressions}), or an invocation of an equality operator on either \SUPER{} or an expression $e_1$, with argument $e_2$.
 
 
 \LMHash{}
 Evaluation of an equality expression $ee$ of the form \code{$e_1$ == $e_2$} proceeds as follows:
 \begin{itemize}
 \item The expression $e_1$ is evaluated to an object $o_1$.
 \item The expression $e_2$ is evaluated to an object $o_2$.
-\item If either $o_1$ or $o_2$ is \NULL{}, then $ee$ evaluates to \code{identical($o_1$, $o_2$)}.  Otherwise,
+\item If either $o_1$ or $o_2$ is \NULL{}, then $ee$ evaluates to \TRUE{} if both $o_1$ and $o_2$ are \NULL{} and to \FALSE{} otherwise.  Otherwise,
 \item $ee$ is equivalent to the method invocation \code{$o_1$.==($o_2$)}.
 \end{itemize}
 
 
 \LMHash{}
 Evaluation of an equality expression $ee$ of the form \code{\SUPER{} == $e$} proceeds as follows:
 \begin{itemize}
 \item The expression $e$ is evaluated to an object $o$.
-\item If either \THIS{} or $o$ is \NULL{}, then $ee$ evaluates to \code{identical(\THIS{}, $o$)}. Otherwise,
+\item If either \THIS{} or $o$ is \NULL{}, then $ee$ evaluates to evaluates to \TRUE{} if both \THIS{} and $o$ are \NULL{} and to \FALSE{} otherwise. Otherwise,
 \item $ee$ is equivalent to the method invocation \code{\SUPER{}.==($o$)}.
 \end{itemize}
 
 \commentary{As a result of the above definition, user defined \code{==} methods can assume that their argument is non-null, and avoid the standard boiler-plate prelude:
  
  \code{if (identical(\NULL{}, arg)) return \FALSE{};}
 
 Another implication is that there is never a need to use \code{identical()} to test against \NULL{}, nor should anyone ever worry about whether to write \NULL{} == $e$ or $e$ == \NULL{}. 
 }
 
@@ skipping 3025 matching lines @@
 
 The invariant that each normative paragraph is associated with a line
 containing the text \LMHash{} should be maintained.  Extra occurrences
 of \LMHash{} can be added if needed, e.g., in order to make
 individual \item{}s in itemized lists addressable.  Each \LM.. command
 must occur on a separate line.  \LMHash{} must occur immediately
 before the associated paragraph, and \LMLabel must occur immediately
 after the associated \section{}, \subsection{} etc.
 
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