Destructive partial readout

When a logical dimension is not a power of two, the logical space is an encoded subspace of its qubit register. Every physical channel is completed on invalid padded inputs, for example by fixed-state preparation. Logical recovery is tested on $C$, including references; it is not an assertion about arbitrary invalid padded inputs.

An infinite-dimensional decoder or syndrome space need not admit a finite program. Theorem thm:exact still supplies a normal CPTP decoder under its hypotheses.