  Some modified two-slit interference experiments claim to demonstrate a
violation of Bohr's complementarity principle. A typical such experiment is
theoretically analyzed using wave-packet dynamics. The flaw in the analysis of
such experiments is pointed out and it is demonstrated that they do not violate
complementarity. In addition, it is quite generally proved that if the state of
a particle is such that the modulus square of the wave-function yields an
interference pattern, then it necessarily loses which-path information.
