In: Advanced Math
we have the question that 'if F is a field with char 0, prove that prime subfield of F is isomorphic to the field of Q'. I already figure out the answer. BUT from the question I have other question have risen in my brain. 1. what are the official definition of the kernel of a map and the characteristics of a field? 2. what is the link between the kernel and the char? 3. are they equivalent in some context?