GI0016

gaussian_signed_product_commutative

The two actual signed product components are commutative, before any quotient normalization.

Alpha v34 checked-use · first admitted v28 · independently kernel and Lean verified; not Stable

Current library: Alpha v34, 4,223 checked-use theorems; Stable remains 432. Historical first admissions, original proof editions, and non-admitted aliases are preserved. Exact original first-admission records.

The natural-code carrier consists of genuine pairs of the existing signed integers; no new primitive arithmetic is trusted. The theorem constructs quotient, remainder, and actual norm witnesses. Gaussian gcd, unique factorization, and prime classification are separate targets.

Exact theorem in conservative defined notation

∀ a. ∀ b. ∀ c. ∀ d. a · c + b · d = c · a + d · b ∧ a · d + b · c = c · b + d · a

Every linked abbreviation expands hygienically to the identical original native formula.

Definition DAG

none

Actual proof prerequisites

mul_comm · checked external prerequisiteadd_comm · checked external prerequisite
Original expanded first-order statement 
forall a b c d. (((((((a) * (c))) + (((b) * (d))))) = (((((c) * (a))) + (((d) * (b)))))) /\ ((((((a) * (d))) + (((b) * (c))))) = (((((c) * (b))) + (((d) * (a)))))))

Complete tactic proof in conservative notation

All 7 original proof lines are preserved. Only local proposition formulas are abbreviated; every abbreviation has an exact binder-safe expansion check. The linked exact edition contains the unchanged replay script.

Read the argument

Proof checkpoints

7 script commands · 3 reading checkpoints · 0 local claims

This is a reading aid, not a new proof or a proof-tree certificate. Checkpoint groups are consecutive commands, not inferred branch boundaries. Every step links to the preserved script.

Definition notation is shown below. Open the paired exact edition for the original native formulas. Source pairing is not a new equivalence certificate.

01Fix variables and assumptionsL1–4

Work with arbitrary variables or the premises of the current implication.

  1. L1
    intro a
  2. L2
    intro b
  3. L3
    intro c
  4. L4
    intro d
02Separate the logical casesL5–5

Follow the explicit conjunction, disjunction, witness, or contradiction step recorded below.

  1. L5
    split
03Calculate and transport equalitiesL6–7

Carry out the recorded arithmetic or equality steps; inspect the exact commands for their direction and premises.

  1. L6
    simp [mul_comm, add_comm]
  2. L7
    simp [mul_comm, add_comm]

Library-wide reading audit

Original defined command ledger · 7 lines
  1. 0001intro a
  2. 0002intro b
  3. 0003intro c
  4. 0004intro d
  5. 0005split
  6. 0006simp [mul_comm, add_comm]
  7. 0007simp [mul_comm, add_comm]