for example (@pxref{Complex expressions}), do @emph{not} evaluate if applied
to such symbols. Likewise @code{log(exp(x))} does not evaluate to @code{x},
because of the unknown imaginary part of @code{x}.
-On the other hand, if you are sure that your symbols will hold only real values, you
-would like to have such functions evaluated. Therefore GiNaC allows you to specify
+On the other hand, if you are sure that your symbols will hold only real
+values, you would like to have such functions evaluated. Therefore GiNaC
+allows you to specify
the domain of the symbol. Instead of @code{symbol x("x");} you can write
@code{realsymbol x("x");} to tell GiNaC that @code{x} stands in for real values.
+@cindex @code{possymbol()}
+Furthermore, it is also possible to declare a symbol as positive. This will,
+for instance, enable the automatic simplification of @code{abs(x)} into
+@code{x}. This is done by declaying the symbol as @code{possymbol x("x");}.
+
@node Numbers, Constants, Symbols, Basic concepts
@c node-name, next, previous, up