The behavior of most modern eye doctors is still based on the idea that optics is a closed field.

Over any algebraically closed field, there is just one Albert algebra.

Because of this fact, C is called an algebraically closed field.

However, there are no primitive 3rd roots of unity in a real closed field.

Any extension of an algebraically closed field is weakly C.

Let C be an algebraically closed field and x a variable.

They tie the whole space into a closed field.

Assume from now on that is a real closed field.

More generally, any real closed field has Brauer group of order two.

The real numbers are not, however, an algebraically closed field.