  We derive a single-channel effective Kbar N interaction from chiral SU(3)
coupled-channel dynamics, emphasizing the important role of the pi Sigma
channel and the structure of the Lambda(1405) resonance. The chiral low energy
theorem requires strongly attractive interaction not only in the Kbar N channel
but also in the pi Sigma channel. As a consequence of the strong pi Sigma
dynamics, the equivalent potential in single Kbar N channel turns out to be
less attractive than the one used in a purely phenomenological approach.
