  We analyze Einstein's recoiling slit experiment and point out that the
inevitable entanglement between the particle and the recoiling-slit was not
part of Bohr's reply. We show that if this entanglement is taken into account,
one can provided a simpler answer to Einstein. We also derive the
Englert-Greenberger-Yasin duality relation from this entanglement. In addition,
we show that the Englert-Greenberger-Yasin duality relation can also be thought
of as a consequence of the sum uncertainty relation for certain observables of
the recoiling slit. Thus, the uncertainty relations and entanglement are both
an integral part of the which-way detection process.
