Implement degeneracy map detection and factorisation

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Core degeneracy infrastructure from the LICS 2022 paper:

- Simple degeneracy detection: Checks that the singular map is injective
  (composition of face maps) and all slice maps are identities.

- Parallel degeneracy detection: Checks that the singular map is the
  identity (no cones in RewriteN) and all slice maps are degeneracies.

- Degeneracy detection: Combines simple and parallel checks.

- Factorisation (Lemma 7): Every degeneracy factors uniquely as
  N --simple--> P --parallel--> T.

- Pullback computation (Proposition 13): Given degeneracies f: X -> T
  and g: Y -> T, computes the pullback by intersecting images in Delta+.

- Helper functions: simple_degeneracy_at(), extract_singular_map(), etc.

All 53 tests pass.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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Maximus Gorog 2026-04-07 02:56:55 -06:00

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