Lectures onType Theory
Extensional, homotopical, and computed equality deltas
appendix sectionsignatures

Extensional, homotopical, and computed equality deltas

TH, TE, and TI.

TH is the universe-free Π/Σ/1/N/Id Hofmann core. TE adds reflection and identity uniqueness; TI instead adds UIP and function-extensionality constants. Theorem 35.39 compares inhabitation only at this signature. It is not a conservativity theorem for T0. Separately, theorem 90.48 imports the Kapulkin–Li Morita equivalence between contextual-category models with Id, ΠExt, Σ, and UIP, and the matching extensional models. Morita equivalence here means the displayed free–forgetful Quillen adjunction has weak-equivalence unit at cofibrant models. It covers cofibrant extensions at that signature; it is neither blanket syntactic conservativity nor support for Tfam or Tco.

Thott.

Add universe-indexed univalence, its derived function extensionality, truncations, and only the displayed HIT signatures. Univalence is axiomatic and does not compute. The simplicial-model consistency import is exact; no normalization theorem is claimed.

TTobs.

Replace ordinary equality use by the displayed observational equality and cast rules. Normalization/canonicity claims are exactly those imported from the Pujet–Tabareau signature; the chapter’s finite Kappa companion is implemented only.

De Morgan cubical.

Add De Morgan dimensions, face formulas, systems, composition, and Glue. Univalence computes through Glue. The cited canonicity/normalization results apply only at their stated cubical signatures.

Cartesian cubical.

Replace De Morgan dimension operations by Cartesian substitution and diagonal cofibrations; use arbitrary-source coercion, homogeneous composition, and V/Kan universes. Computational soundness and canonicity are exact imports from Angiuli’s operational semantics; normalization is exactly imported from Sterling–Angiuli only for their universe-free Π/Σ/path/Glue/circle calculus CSA. The source explicitly omits universes and does not prove its stated De Morgan adaptation. These imports do not make either extension, or any omitted rule, derivable.

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