pub const BABYBEAR_S_BOX_DEGREE: u64 = 7;
S-box degree for BabyBear Poseidon1.
Since p - 1 = 15 * 2^27, both 3 and 5 divide p - 1.
p - 1 = 15 * 2^27
p - 1
So gcd(α, p - 1) ≠ 1 for α ∈ {3, 5}. The next smallest valid exponent is 7.
gcd(α, p - 1) ≠ 1
α ∈ {3, 5}