Weak hadronic decays:K→2πandK→3π

We present a phenomenological review of the weak hadronic decay processes $K\mu 2\pi$ and $K\to 3\pi$, primarily the $\mathrm{CP}$-conserving transitions. We have paid particular attention to consistency between different experimental measurements of the same quantity. We have performed a least-squares analysis of the data to determine transition amplitudes to various final states, and the dependence on final-state energy variables. Tests of isotopic spin selection rules have been made by applying various constraints to the least-squares analysis. Amplitudes for pure isotopic spin transitions to specific final states are presented. Current algebra predictions are remarkably well satisfied for the pure $\Delta I=\frac{1}{2}$ amplitude.