ORA-FO-EXCEPT 15.2.5 op:except

*Functions and Operators, Section 15.2.5 op:except* "Constructs a 
sequence .... eliminating duplicate nodes"

If there are duplicates in $parameter1, do they get eliminated ?
If so, do the duplicates in $parameter1 get eliminated even when 
$parameter2 is the empty sequence ?

What about op:union, op:intersect - are duplicates in one of the input 
sequences preserved or eliminated ?