The prime subfield of a field 
is the subfield of 
generated by the multiplicative identity 
of 
. It is isomorphic to either 
(if the field characteristic
is 0), or the finite field 
(if the field characteristic
is 
).
Prime Subfield
See also
SubfieldExplore with Wolfram|Alpha
References
Dummit, D. S. and Foote, R. M. "Basic Theory of Field Extensions." §13.1 in Abstract Algebra, 3rd ed. Hoboken, NJ: Wiley, pp. 510-519, 2004.Referenced on Wolfram|Alpha
Prime SubfieldCite this as:
Weisstein, Eric W. "Prime Subfield." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PrimeSubfield.html