ENH: updates from Tom and Humphrey (#410)

* update minor typos

* update notes and typos

* update

* update fix and notes

* Tom's edits of ge_arrow lecture in intermediate repo

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Co-authored-by: Humphrey Yang <u6474961@anu.edu.au>
Co-authored-by: thomassargent30 <ts43@nyu.edu>

Author: 3 people