Alphabeta Math
CounterexampleConstruction: Literature-sourcedVerification: AI-adaptedSession-authored (Fable 5 assisted)precheck passaudited 2026-08-13 rests on unproved material (inherited)
How statement and proof provenance work

The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.

  • Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
  • AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.

These labels describe origin, not correctness: citations and verification chips remain separate evidence.

Rests on 3 statements not proved in this library, by way of the results it cites. This item cites no such statement directly; it depends on results that do. The unproved premises it inherits are Cohen's first model: an infinite Dedekind-finite set of reals, Sierpiński 1947: the generalised continuum hypothesis implies the Axiom of Choice and The continuum hypothesis and its generalisation are independent of ZFC. Each is recorded with a citation to the literature and is not established here, because the track that would prove it has not yet been developed in this library. Everything else in this proof is proved here.

Assuming Choice, nonempty sets have all small products but a parallel pair with no equalizer and hence a diagram with no limit

Statement refuted

If a category has all small products, then it has all small limits.

Facts & Assumptions

Given: The full category Set of nonempty sets and all functions between them, under the Axiom of Choice.

[F1]
[F3]

Choice is equivalent to nonemptiness of a product of an arbitrary family of nonempty sets (The Axiom of Choice).

Counterexample

technique · missing equalizer
1.1

The ordinary Cartesian product of any set-indexed family of nonempty sets is nonempty by [F3] and has the product property [F1] inside the full subcategory. For the empty family, the singleton is a nonempty terminal object. Thus Set has all small products.

F1F3
1.2

Let f,g:{}{0,1} be the constant maps with values 0 and 1. If h:X{} equalized them, then fh and gh would be the distinct constant functions on the nonempty set X. Hence no equalizing cone exists in Set, so in particular no equalizer [F2] exists.

F2given
2.1

The parallel-pair diagram is finite and small but has no limit, refuting the statement. This is exactly the missing equalizer data isolated by [L1].

L1step 1.1step 1.2

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 17 results over 9 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.

Sources