The finite geometric series partial-sum identity over the constructed reals

Identifier: F:creal-mul-sub-one-geom
Proof route: kernel-lean
External status: proved
Axiom footprint: Empty

Recorded description

For a constructed real x and natural n, (1 - x) * sum_{i<n} x^i is CReal.Equiv-equivalent to 1 - x^n. The finite geometric-series telescoping identity, the algebraic core geometric convergence proofs are built on.

Formal statement

theorem CReal.mul_sub_one_geom : ((x0 : CReal) -> ((x1 : AxNat) -> CReal.Equiv (CReal.mul (CReal.add CReal.one (CReal.neg x0)) (CReal.sumRange (fun (x2 : AxNat) => CReal.pow x0 x2) x1)) (CReal.add CReal.one (CReal.neg (CReal.pow x0 x1)))))

Dependencies

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14 direct dependencies 2 direct dependents Graph shows the first 8 on each side.

Evidence

kernel-CReal.mul_sub_one_geom

Kind: kernel-term
Status: checked

Supports: CReal.mul_sub_one_geom is admitted by the trusted kernel gate with the type recorded in formal.statement.

Checker command

cargo run -q --release -p axeyum-lean-kernel --example theorem_dependency_inventory -- CReal.mul_sub_one_geom 2>/dev/null | grep -cE '^CReal\.mul_sub_one_geom[[:space:]]'

Evidence notes

`build_creal_prelude` admits CReal.mul_sub_one_geom through the trusted `Kernel::add_declaration` gate, which re-checks the proof term against the stated type, so a line in this tool's output for the exact name is a machine-checked proof having been admitted. `theorem_dependency_inventory` was extended in this same change to build creal/complex/cpoint (previously only nat/integer/rat/string/characterization); it exits non-zero for a named filter that matches nothing, and `grep -c` (never `-q`) independently asserts the exact tab-anchored line is present. `--release` is MANDATORY: building the constructed carriers recurses deep enough in a debug build to overflow the default thread stack (measured: release exits 0 with 1092 theorems total, debug SIGABRTs at 134) -- the same resource-limit gotcha already documented for `prelude_theorem_inventory --include-constructed`.

footprint-CReal.mul_sub_one_geom

Kind: exhaustive-enumeration
Status: checked

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

Checker command

cargo run -q --release -p axeyum-lean-kernel --example nat_axiom_inventory -- --include-constructed --require-axiom-free creal

Evidence notes

`nat_axiom_inventory --include-constructed` builds the CReal environment as its own group and reports `creal: axiom=0 opaque=0 quotient=0 total_trusted=0` (re-measured on this tree). That bounds every individual CReal theorem's footprint by [], since a theorem cannot depend on a trusted declaration the environment does not contain, and the enumeration covers Axiom, Opaque AND Quotient, not just Declaration::Axiom. `--include-constructed` is REQUIRED here -- without it `--require-axiom-free creal` is an error (verified: exit 1), not a silent pass, because creal is not built at all without the flag; this is the standing trap of an empty/absent result reading as a strong negative when the tool was never pointed at the subject.

Provenance

{
  "date": "2026-08-25",
  "established_by": "axeyum-lean-kernel build_creal_prelude",
  "source": "theorem name and dependency edges from theorem_dependency_inventory (extended in this change to cover creal/complex/cpoint); canonical type read via a standalone probe binary depending on axeyum-lean-kernel by path, calling only its public Kernel API (environment(), display_name(), render_lean(), axiom_footprint()) -- no in-tree example currently prints CReal theorem types, and crates/ source was left untouched here beyond theorem_dependency_inventory.rs itself."
}