Structure of 1,4-Difluorobenzene

How many structure isomers exist for difluorobenzene?
There are three and they are the ortho, meta and para isomers. Shown here is the 1,4-difluorobenzene or para-difluorobenzene.


Figure. The RHF/6-31G* optimized structure of 1,4-difluorobenzene.