You are comparing the nodes for equality, whereas your description suggests
you want to compare them for identity. To compare whether $A and $B are the
same node, use ($A is $B) in XPath 2.0, or (count($A|$B)=1) in XPath 1.0.

That's exactly what i want. In fact, testing for equality could lead to
potencial errors, cause nothing in my structure forbids the existence of
two nodes with the same content.