let 'Nextperson' be a proper name for the next person who goes through that door (if there is such a person). Still for any Nextperson, it is contingent whether or not he went through the door. So the definition of Nextperson is a contingent, a priori truth. A definite description can "fix the reference" but it does not "give the meaning", i.e., it is not synonymous with the name