You can achieve fair results even from slightly biased coins (or unknowingly biased tossing habits):
- Toss the coin twice.
- If the results match, start over, forgetting both results.
- If the results differ, use the first result, forgetting the second.
Actually, the von Neumann method even works with extremely biased coins, it will just take more time and tosses to get enough valid outcomes.
Fundamentally, it just relies on basic probability laws :
p(HT) = p(H) x p(T) = p(TH) and
p(H) + p(T) = 1so
p(T) = 1 - p(H) p(HT) = p(TH) = p(H) x (1 - p(H)) The probability is the same for HT and TH whatever p(H) and p(T) are. So even if p(H)=99%, we will get the exact same likelihood to get HT and TH. In the same way as for H and T with a perfect fair coin. Then if you only keep HT and TH you will likely get half HT and TH among all the retained tosses, and finally half H and T if you forget the second outcome.
So it's certainly the easisest safest method to create a seed if you use it along with Odolvlobo's procedure IMO.