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First page of Recursive Completion in Higher K-Models: Front-Seed Semantics, Proof-Relevant Witnesses, and the K-Infinity Model

Recursive Completion in Higher K-Models: Front-Seed Semantics, Proof-Relevant Witnesses, and the K-Infinity Model

Daniel O. Martinez-Rivillas, Arthur F. Ramos, Ruy J. G. B. de Queiroz

cs.LO Apr 14, 2026 · v1
Fully formalizes higher K-model semantics in Lean 4 (no sorry/admit/axiom).
Martinez-Rivillas and de Queiroz gave extensional Kan semantics for the untyped lambda-calculus and later constructed the concrete K-infinity homotopy-model. The two main mathematical results of the present paper are these. First, we show that a smaller front-seed coherence package (WL, WR) together with an inner-right-front pentagon contraction already suffices to recover the associator comparison, semantic pentagon, and bridge theorems used in the later semantic arguments. Second, we prove explicit global reify, reflect, and application formulas for K-infinity, with exact coordinatewise identities at every finite stage. We also record two structural clarifications: the recursive all-dimensional continuation of the explicit low-dimensional tower is obtained by a finite packaging phase followed by a uniform equality-generated recursion; and, on a deliberately fixed forward witness language for the classical separation span, the canonical identity-type higher tower on K-infinity forces all higher non-connection once the two witness classes land at distinct points. The paper is fully formalized in Lean 4, and the project sources contain no local uses of sorry, admit, or axiom.

Martinez-Rivillas and de Queiroz constructed extensional Kan semantics and a K-infinity homotopy-model for the untyped lambda-calculus, but the coherence requirements and explicit formulas for the recursive completion remained unverified at higher dimensions.

The paper shows that a smaller front-seed coherence package (WL, WR) with an inner-right-front pentagon contraction suffices to recover the associator comparison, semantic pentagon, and bridge theorems. Explicit global reify, reflect, and application formulas for K-infinity are proved with exact coordinatewise identities. Select coherence lemmas at dimensions 4-6 are verified in Lean.

The front-seed reduction shows that three chosen 3-cells (two front witnesses and one contraction) suffice to derive the full coherence structure. Exact coordinate formulas for the K-infinity model are established, and the Lean verification confirms the combinatorial coherence arguments at the critical low dimensions.