I'm not claiming that if something exists (haemoglobin), we must have a notion of it and true statements about it in every universe. Rather: if we have a notio

I'm not claiming that if something exists (haemoglobin), we must have a notion of it and true statements about it in every universe. Rather: if we have a notion of something and statements about it in every universe, then it must exist. However, come to think of it, that's bonkers. Still, it's remarkable that mathematics allows us to make reproducible true statements about fictional objects.