  We use a twice-subtracted partial-wave dispersion relation in the elastic
unitarity approximation for final-state interactions to study the amplitude for
the delta I = 1/2 CP-conserving weak process K+spurion->pi+pi. We use a simple
parameterization to approximate the low energy I = 0 S-wave pipi->pipi
scattering phase shift and extract the residue of the sigma pole in the weak
amplitude obtained from the dispersion relation. Using this residue, we relate
the K->pipi decay amplitude, the weak amplitude at the soft pion point and the
K->sigma weak amplitude.
