One stage of the interface recursion, with the matchings supplied #
The per-glue ledgers ask for two matchings and a handful of equations between their pairings. In the recursion both matchings pair by an involution of the labels — the chord matching by the subset's chords, the interface matching by the swap — and the equations are then automatic. This file states each stage with the interface matching given that way, so that a stage consumes only the involution and the one equation saying the glued labels are partners.
One stage at an open cut the subset uses. The circuit count and the number of components of the union move together.
One stage at an open cut the subset misses. Nothing moves: the two glued labels are unused, so the chord matching and the interface matching both simply transport.
One stage at a closed cut the subset carries. One component of the union disappears, into the free circle the glue creates.
One stage at a closed cut the subset leaves out. Nothing moves; the free circle the glue creates carries no chord.
The two cut kinds, each in one statement #
Whether the subset uses a cut is decided by the data, not by the caller, so each kind of cut is better stated once: an open cut moves nothing either way, and a closed one drops a component exactly when the subset carries its edge.
One stage at an open cut. Nothing moves, whether or not the subset uses the cut.
One stage at a closed cut. A component of the union disappears exactly when the subset carries the cut's own edge.
Pairing across a glue #
Both glues read a surviving label as a label, so the pairing record transports as soon as the glued swap does — one equation between label maps, with the subset's own data nowhere in it.
Pairing across a closed glue.
Pairing across an open glue.