Field has Prime Subfield

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Let $\struct {F, +, \times}$ be a field.

Then $F$ has a subfield which is a prime field.


By definition of field, $F$ is a division ring where $\times$ is commutative.

Therefore all division subrings of $F$ are in fact subfields of $F$.

By Intersection of All Division Subrings is Prime Subfield, the intersection of all subfields of $F$ is a prime field which is a subfield of $F$.