Could someone please verify whether my solution is okay? It seems kind of short and I am not sure if I should add more to it.
Let $I$ be an ideal in a ring $R$. Show that the ring homomorphism $\phi:R\to R/I$ defined by $\phi(r)=r+I$ is well-defined.
Well-defined: Let $r,s\in R$. Then if $r=s$, $\phi(r)=r+I=s+I=\phi(s)$.
Should I add more to this or is it valid?