theorem :: FIELD_9:72

for F being non 2 -characteristic Field
for E being FieldExtension of F holds
( deg (E,F) = 2 iff ex a being Element of F st
( ( for b being Element of F holds not a = b ^2 ) & ex b being Element of E st
( a = b ^2 & E == FAdj (F,{b}) ) ) )