TheoremStatement: Literature-sourcedProof: AI-adaptedSession-authored (Fable 5 assisted)precheck passaudited 2026-08-29‡ 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.

Monicity is detected by members

Statement

For a morphism $f : A \to B$ in an abelian category, the following are equivalent:

$f$ is monic.
For every member $x : X \to A$ , the implication $f x \equiv 0 ⟹ x \equiv 0$ holds.

Facts & Assumptions

Given: A morphism $f : A \to B$ .

[L1]

Monomorphisms are left-cancellable (Monomorphism and epimorphism by left and right cancellation).

[L2]

A member equivalent to zero is literally the zero morphism, and every member has a zero comparison member (Each object has a zero member and each member has a negative).

[L3]

Postcomposition preserves member equivalence (A morphism carries members to members and preserves equivalence).

Proof

technique · direct

1.1

Assume $f$ is monic, and let $x : X \to A$ satisfy $f x \equiv 0$ . Choose an epic $u : W \to X$ witnessing this, so $f x u = 0$ . Since $f$ is monic, $x u = 0$ , and the same epic $u$ witnesses $x \equiv 0$ .

L1L2assume-hypalgebra

1.2

Assume condition 2. If $u, v : U \to A$ satisfy $f u = f v$ , then for the member $x : = u - v$ one has $f x = f u - f v = 0$ , hence $f x \equiv 0$ by [L2] and [L3]. Condition 2 gives $x \equiv 0$ , so [L2] makes $x = 0$ , namely $u = v$ . Thus $f$ is monic by [L1].

L1L2L3assume-hypalgebra

2.1

Therefore the two conditions are equivalent.

step 1.1step 1.2∎

Depends on

Used by

A member chase verifying monicity Example
Monicity by member cancellation Theorem

Dependency tree · two levels

8 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.

Sources

Saunders Mac Lane, Categories for the Working Mathematician, Theorem VIII.4.3(i) (standard reference, not scraped)