  We study the decays $K\to\pi\pi$ in one-loop two-flavour Chiral Perturbation
Theory. We provide arguments why the calculation of the coefficient of the
pionic chiral logarithm $\logm = M^2\log M^2$ is unique and then perform the
calculation. As a check we perform the reduction of the known three-flavour
result. The underlying arguments are expected to be valid for heavier particles
and other processes as well.
