parity (0,0) — even-even
parity (1,0) — x odd, y even (← base candidates)
parity (0,1) — x even, y odd (← apex candidates)
parity (1,1) — both odd
σ = + (Harnack: parity (0,0) by default)
σ = − (Harnack: all other parities)
sign flipped by selected twist
Simple splits
(0, y)–(x, 0) with x, y odd, x ≥ y
Double splits
(x₁, 0)–(x₂, y)–(x₃, 0) with x₁ < x₃ odd, x₂ even ≥ 2, y odd
| (x₁, x₂, x₃, y) |
A |
B |
m |
proof? |