An inaccuracy in slides 35, 36:
  Bitcoin nodes will converge on the blockchain that was the
  most difficult to produce (in terms of the computational power that was required),
  and not simply on the longest one.

  This is required since the difficulty of producing a block can vary depending
  on how much computational power the entire bitcoin network possesses.

  The blockchain that was most difficult to produce will most of the times be the longest
  one, so it's a "good enough" approximation of which blockchain wins, but not entirely
  accurate.