A2
= A2
{c}
{scope}
The <characteristic of a field>[characteristic] is the least positive integer $r$ with $r1_K=0$, if it exists, and zero otherwise. The <prime> subfield is the smallest subfield containing $1_K$; in <characteristic of a field>[characteristic] $p$ it is $F=\{0,1,\ldots,(p-1)1_K\}\cong\mathbb F_p$. Every <field automorphism> fixes $1_K$ and addition, so it fixes every element of this <prime> subfield.