Note learning prerequisites

Hi
I think we should have an option to link notes with others in a way that a note doesn’t show up until you learn the notes linked to it
This is useful in math when learning something new in shared decks
For example:
Note a:
\(\overrightarrow{a}\cdot\overrightarrow{b}=\vert\overrightarrow{a}\vert\cdot\vert\overrightarrow{b}\vert\cdot\cos\theta\)
Note b:
\(\cos\theta=\frac{\overrightarrow{a}\cdot\overrightarrow{b}}{\vert\overrightarrow{a}\vert\cdot\vert\overrightarrow{b}\vert}\)

Note b in this case wouldn’t show up until you learn note a because you get b from a.

In theory this is pretty easy. You could write an addon with a button/shortcut that allows you to add a tag that contains the guid of a prerequisite note. Then you’d have to patch the review/new card order sorting logic so that it also does some sort of topological order according to the prerequisite graph. Some preliminary work has been done on this.