Descending extensions in the punctured normal-jet module

The only module in the record with defined presentations, reconstruction, canonical domain, and target is the finite normal-jet module with punctured reconstruction of XV-D XVD. XV-D computed the null defect of every extension lift and exhibited a nonzero defect cancelled by a change of extension. XV-E now determines exactly which relations carry a defect and when a descending extension exists. Everything in this section concerns that module; it is not identified with ${\mathcal{P}}_{\mathrm{int}}$.