Read a book in hospital about the FD 2, it is true, that the design was copied, in point of fact if you overlay the two aircraft they are "identical" in dimensions.
The book says " in the autumn of 1956 it (FD 2) spent a month based at Casuax, near the west coast of France, and flew supersonically at heights down to 3,500ft, which would have been forbidden in Britain. It was here that that Marcel Dassault decided that this was the shape to go for, and designed the Mirage III as a radar-equipped FD 2.