the kernel is defined as a set in this text and I'm told to prove it is a subgroup of something. So, I was wondering if a set could be a subgroup without an operation explicitly defined @0celo7
isn't the kernel of a homomorphism just a set of 1 element? Say $G,H$ are groups $\varphi:G \to H$ is a homomorphism. The kernel of $\varphi$ is $\{g \in G~|~\varphi(g) = I_H\}$ isn't there only 1 element in this kernel, which is the identity element in $G$? Like say $\varphi(ab) = \varphi(a)\varphi(b)$ where $\varphi(b) = I_H$ then $\varphi(ab) = \varphi(a)I_H$ only 1 $b$ such that $\varphi(ab) = \varphi(a)$?
@danu I don't see what you mean by the trivial homomorphism. If there are multiple elements in $G$ that the image of which is the identity in the target set, doesn't that mean $G$ has multiple identity elements?
how can $\varphi(gh) = \varphi(g)\varphi(h)$ be satisfied where multiple elements $g \in G$ satisfy $\varphi(g) = I_H$ without $g$ being the identity in both $G,H$?
en.wikipedia.org/wiki/Kernel_(algebra) here it shows (under group homomorphisms) that its only injective if and only if the kernel is the singleton set $\{e_g\}$