Pith. sign in
theorem

circleH1ZIsoInt_of_rawPrism

proved
show as:
module
IndisputableMonolith.Foundation.CircleWindingChain
domain
Foundation
line
7367 · github
papers citing
none yet

plain-language theorem explainer

A raw prism filling for every oriented cyclic family on the circle yields the Mathlib identification H₁(S¹;ℤ) ≅ ℤ. Anyone finishing the generation half of the singular homology computation cites this reduction step. The proof is a one-line composition: transport the raw-prism hypothesis to cycle-boundary generation, then apply the oriented-family criterion.

Claim. Assume decidable equality on singular $0$-simplices and $1$-simplices of $S^1$. If every oriented cyclic family admits a raw prism filling (a singular $2$-chain whose boundary equals the oriented closed walk minus an integer multiple of the fundamental cycle), then $H_1(S^1;\mathbb{Z})\cong\mathbb{Z}$ via the Mathlib singular-homology comparison.

background

This module lifts the path-level winding/displacement invariant of the circle to singular simplices of TopCat.sphere 1 and proves that winding kills boundaries: for every singular $2$-simplex the alternating face sum of displacements vanishes. Together with the fact that the once-around generator has winding $1$, that gives the split-injective half of $H_1(S^1;\mathbb{Z})\cong\mathbb{Z}$. The remaining generation half (every $1$-cycle homologous to an integer multiple of the fundamental cycle) needs a simplicial prism/subdivision operator that Mathlib singular homology does not yet supply.

The raw-prism generation hypothesis states exactly the chain-level prism target an explicit construction should hit: for each oriented cyclic family term $T$, there exist an integer $n$ and a singular $2$-chain $b$ with $\partial b$ equal to the directed cycle of $T$ minus $n$ times the fundamental cycle (as a cycle object). Singular $0$- and $1$-simplices are the actual vertices and edges of the singular simplicial set of $S^1$.

Upstream, boundary generation from raw prisms is pure categorical transport through the inclusion of cycles; the oriented-family criterion then reduces the Mathlib circle $H_1$ isomorphism to that generation statement.

proof idea

One-line term-mode wrapper. First apply orientedCyclicFamilies_boundary_generate_of_rawPrism to the raw-prism hypothesis, obtaining the cycle-object generation target (for each oriented cyclic family, a $2$-chain whose boundary realizes the closed walk minus a multiple of the fundamental cycle, after transport into cycles). Then feed that into circleH1ZIsoInt_of_orientedCyclicFamilies, which itself reduces through the fundamental-cycle generation lemma to the Mathlib bridge isomorphism circleH1ZIsoInt. No new algebraic work occurs here.

why it matters

This is the middle rung of the prism-generation ladder that closes the surjectivity half of $H_1(S^1;\mathbb{Z})\cong\mathbb{Z}$ against Mathlib's singular homology. Downstream, circleH1ZIsoInt_of_explicitRawPrism specializes the hypothesis further to a fully explicit raw-prism filling and cites this theorem as the sole step. The module doc frames the open gap: Mathlib lacks a built-in simplicial prism/subdivision operator, so the project must supply generation by hand; this declaration isolates that remaining obligation at the raw-chain level rather than at the more abstract cycle-object level. In the Recognition foundation stack it anchors the winding homomorphism as a true homology invariant with integer comparison, the topological backbone for later octave and forcing-chain arguments that treat $S^1$ periods as discrete recognition ticks.

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