Mathlib v4.30 source proposition Nat.dist.triangle_inequality

Identifier: F:ml430-nat-dist-triangle-inequality-b35e82d3
Proof route: kernel-lean
External status: proved
Axiom footprint: Empty

Recorded description

The proposition declared as `Nat.dist.triangle_inequality` in the pinned Mathlib v4.30 source.

Formal statement

∀ (n m k : ℕ), n.dist k ≤ n.dist m + m.dist k

Dependencies

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12 direct dependencies 0 direct dependents Graph shows the first 8 on each side.

Evidence

kernel-Nat.dist_triangle_inequality

Kind: kernel-term
Status: checked

Supports: ∀ (n m k : ℕ), n.dist k ≤ n.dist m + m.dist k

Checker command

test "$(cargo run -q --release -p axeyum-lean-kernel --example nat_theorem_inventory -- dist_triangle_inequality 2>/dev/null | grep -Ec '^Nat\.dist_triangle_inequality[[:space:]]')" -ge 1

Evidence notes

`build_nat_prelude` admits `Nat.dist_triangle_inequality` (`nat_prelude/dist_more2.rs`) through the trusted `Kernel::add_declaration` gate. `nat_theorem_inventory`'s rendered type is `(x0 x1 x2 : AxNat) -> AxNat.le (dist x0 x2) (add (dist x0 x1) (dist x1 x2))`, matching this fact's `formal.statement` up to variable naming. The kernel name drops Mathlib's `.triangle_inequality` namespace suffix (this prelude does not model dotted sub-namespaces) but states the identical proposition. Anchored with `^Nat\.dist_triangle_inequality[[:space:]]`; `grep -Ec` consumes the pipe so the tested count decides the exit status. Run `--release` -- the debug build of this inventory example SIGABRTs on stack depth (unrelated to this proof).

compute-Nat.dist_triangle_inequality

Kind: kernel-term
Status: checked

Supports: n=1,m=5,k=2 (dist(1,2)=1 <= dist(1,5)+dist(5,2)=4+3=7, exercising the internal `Le n k` branch) and n=8,m=1,k=3 (dist(8,3)=5 <= dist(8,1)+dist(1,3)=7+2=9, exercising the `Le k n` branch) -- two instances covering BOTH sides of the proof's internal case split.

Checker command

cargo test -p axeyum-lean-kernel --lib nat_prelude::nat_prelude_tests::dist_triangle_inequality_applies_at_concrete_instances

footprint-Nat.dist_triangle_inequality

Kind: exhaustive-enumeration
Status: checked

Supports: axiom_footprint: [] -- the Nat prelude's trusted surface is empty

Checker command

cargo run -q --release -p axeyum-lean-kernel --example nat_axiom_inventory -- --require-axiom-free nat

Evidence notes

`nat_axiom_inventory --require-axiom-free nat` enumerates the built Nat environment and exits non-zero unless it admits no Axiom, Opaque or Quotient declaration (measured: axiom=0 opaque=0 quotient=0). A theorem cannot depend on a trusted declaration the environment does not contain, so an empty trusted surface bounds `Nat.dist_triangle_inequality`'s footprint by [].

Provenance

{
  "date": "2026-08-30",
  "established_by": "lane draw9-second-theorems",
  "source": "statement-only extraction of `Nat.dist.triangle_inequality` from Mathlib v4.30.0; no proof value was exposed",
  "prior_art": [
    {
      "who": "the Mathlib contributors",
      "what": "the theorem declaration `Nat.dist.triangle_inequality`",
      "where": "mathlib4 commit c5ea00351c28e24afc9f0f84379aa41082b1188f (v4.30.0)",
      "year": 2026,
      "attribution": "the proposition was read from the pinned statement-only inventory; the proof term and tactic trace were not consulted"
    }
  ]
}