\section{Introduction}
This paper presents {\MathQL} version 4 which is the latest version of the
-language, fully developed by Ferruccio Guidi.
+language, fully developed by the Author.
For a description of the previous versions of {\MathQL} see: \cite{Gui03}
(version 3), \cite{GS03} (version 2), \cite{Lor02} (version 1).
+The main novelties of this version are the elimination of some cast operators
+(producing a substantial simplification in the query structure and semantics),
+a clear distinction between the core language and the auxiliary functions of
+the basic library, a support for query generating functions, the possibility
+of extending the language adding new libraries of functions and a more uniform
+textual syntax.
+{\MathQL}.4 incorporates the features of {\MathQL}.3 not documented on paper%
+\footnote
+{See the ``what's new'' section of {\MathQL} Web Site:
+\CURI{helm.cs.unibo.it/mathql}.}
+and adds some new features improving {\MathQL} capabilities to post-process
+the query results.
+
+\input{mathql_introduction_avsets}
+\input{mathql_introduction_property}
+\input{mathql_introduction_core}
+\input{mathql_introduction_basic}
+\input{mathql_introduction_textual}