Choi and complementary-channel comparisons

For finite complementary channels, the KSW information–disturbance theorem KSW (Theorem 3) implies, in the present half-diamond convention,

Indeed, in full-diamond normalization the recovery-to-leakage direction gives

and the opposite direction gives the analogous bound with recovery and leakage exchanged. Division by two yields (eq:KSW). This is a channel conversion, not a magic theorem or a dynamical estimate.