Unit vector notation - both line and hat? I know that unit vectors are usually written in bold with a hat for example: $$\hat{\mathbf{i}}$$
But if you use vector notation with arrows (as I do when I write with pen and papper), should you both have an arrow above the vector and a hat, or just the hat?
Thanks!

In general, what indicates whether a vector is unit vector or not is the letter used rather than the hat ($\hat{}$). So, as long as you prevent confusion by not giving name $i,j,k,e_1,e_2$ etc. to some other vectors, $\vec{i}$ still is a unit vector. But I should also note that this also depends on the context in which you are using this notation. I don't know whether there is a context where $\hat{i}$ or $\vec{i}$ is a different vector from $[1\ 0\ 0]^T$ but I am sure that in some contexts, someone can name a vector $i$ even if it is not a unit vector (for instance where $e_1,e_2,e_3,$ etc. are used for unit vectors). But as long as you clarify your notation beforehand, I don't think there will be any problems when you use $\vec{i}, \vec{j}, \vec{k}$
