They are created by simply using the C++ operators @code{==}, @code{!=},
@code{<}, @code{<=}, @code{>} and @code{>=} between two expressions.
-@xref{Mathematical functions}, for examples where various applications of
-the @code{.subs()} method show how objects of class relational are used
-as arguments. There they provide an intuitive syntax for substitutions.
-They can also used for creating systems of equations that are to be
-solved for unknown variables. More applications of this class will
-appear throughout the next chapters.
-
+@xref{Mathematical functions}, for examples where various applications
+of the @code{.subs()} method show how objects of class relational are
+used as arguments. There they provide an intuitive syntax for
+substitutions. They are also used as arguments to the @code{ex::series}
+method, where the left hand side of the relation specifies the variable
+to expand in and the right hand side the expansion point. They can also
+be used for creating systems of equations that are to be solved for
+unknown variables. But the most common usage of objects of this class
+is rather inconspicuous in statements of the form @code{if
+(expand(pow(a+b,2))==a*a+2*a*b+b*b) @{...@}}. Here, an implicit
+conversion from @code{relational} to @code{bool} takes place. Note,
+however, that @code{==} here does not perform any simplifications, hence
+@code{expand()} must be called explicitly.
@node Methods and Functions, Information About Expressions, Relations, Top