Definition: Exceptional block

Fix sites $P,Q$ with $\ell =d(P,Q)>r$. Their ordinary blocks $b_P,b_Q$ are distinct. Replace them by

discarding empty sets. This is a partition.

Channels on the shrunken blocks must be specified anew; a channel on $b_P$ does not automatically restrict to one on $b_P\setminus \{P\}$. Channels of unaffected blocks are retained.

The exceptional block may have a complete instrument supported on its two-site interface. It is record transmissive or name transmissive when it admits the corresponding lossless one-tick transport. It is inert when its complete channel is ${\Phi }_P\otimes {\Phi }_Q$, with no cross-site relocation or classical control.