Spec updated

spec/03.04.expressions.tex

@@ -40,7 +40,7 @@ property ``$e$ is a reference''. The result of assignment operator coincides wit
 assigns 3 to both "\lstinline|x|" and "\lstinline|y|".
 
 \begin{figure}[h]
-  \newcommand{\Ref}[1]{\mathcal{R}\,({#1})}
+  \renewcommand{\Ref}[1]{\mathcal{R}\,({#1})}
   \renewcommand{\arraystretch}{4}
   \[
     \begin{array}{cc}

spec/08.standard_library.tex

@@ -95,6 +95,10 @@ is automatically created and closed within the call.}
 \descr{\lstinline|fun fprintf (file, fmt, ...)|}{Same as "\lstinline|printf|", but outputs to a given file. The file argument should be that acquired
   by \lstinline|fopen| function.}
 
+\descr{\lstinline|stdout|}{Standard output file.}
+
+\descr{\lstinline|stderr|}{Standard error file.}
+
 \descr{\lstinline|fun regexp (str)|}{Compiles a string representation of a regular expression (as per GNULib's regexp~\cite{GNULib}) into
   an internal representation. The return value is a external pointer to the internal representation.}