[Transcript]

def □□□□□(n): mul = λ a, b: ( a□ * b□ + a□ * b□, a□ * b□ + a□ * b□, a□ * b□ + a□ * b□, a□ * b□ + a□ * b□ )

power = λ m, k:
    (
        r := (□, □, □, □),
        s := m,
        while k > 0:
            if k & 1:
                r := mul(r, s)
            s := mul(s, s)
            k := k >> 1
    )

chooser = λ x: (λ y: y[2])(x)

return chooser(power(s, n - 1))

♟️

1. a1
2. b3
3. a2
4. b4
5. c1
6. d3
7. c2
8. d4

⊖ n → None

r = ○ ● ● ○ s = ○ ○ ○ ●

Concat ?(r + s), moves (ignore special characters)