Leave the example,try this :
SSP (Sno, Sname, Pno, Qty)
Here, Sname is considered unique for each Sno.
FD of above relation is
(Sno, Pno) - Qty
(Sname, Pno) - Qty
Sno - Sname
Sname - Sno
This relation has two overlapping candidate keys, because there are two composite candidate keys (Sno, Pno) and (Sname, PNo) out of which Pno is common attribute in both the candidate keys, so this is due case of overlapping of candidate keys.
Here, both the relations are in 3NF, because every non-key attribute is non-transitively fully functional dependent on the primary key.
In above relation, there is only one non-key attribute i.e. Qty and it is FFD and non transitively dependent on the primary key.
Sname, Sno are not non-key attributes because they can participate into the primary key as shown in FD diagram.
But, SSP relation is not in BCNF because this relation has four determinants:
(Sno, Pno)
(Sname, Pno)
(Sno)
(Sname)
Out of these four determinants two determinants (Sno, Pno) and (Sname, Pno) are unique but Sno and Sname determinants are not candidate keys.
So,we see the overlapping candidate keys are causing trouble.... :-)