on the coordinate representation in the dirac bra-ket notation

In this paper we discuss some traps which can occur in using dirac bra-ket notation in the coordinate (or momentum) representation. furthermore, we demonstrate that in order to avoid some misconceptions, it is necessary to distinguish the two operators. first, the ordinary derivative , is just the usual partial differentiation which acts on the scalar function; and should not be considered as an operator which can act on the vectors in the hilbert space. second, unbounded operator , which is usually mixed up with the former. our discussion indicates that the action of these two operators is the same on bra position , but on ket it really leads to different results.