Fix Chapter 1.4 issues

Fixes all the todos you had there
I didn't find anything missing related to the todo unreadable page 18.
I added two packages
mathtools for a nice := and =: (now defined as \defeq and \eqdef respectively)
multicol for the two collumns issue
I also moved the things that were in the 'repetition' but weren't mentioned before into definition 1.9