Typos in Chapter 4; page 170, 172, & 173

[TimSevereijns]

The following is in reference to the 0th Edition, dated Dec. 29th, 2018.

• On page 170, towards the top, I believe it should read:
  • "Unfortunately, resolving one instability can create new ones..."
• On page 172, in the Running Time section, I believe it should read:
  • "How does the algorithm decide whether a doctor prefers her new offer to her current match?"
• On page 173, in the proof, I believe it should read:
  • "Every doctor that appears higher than 𝛼 in B's preference list was already rejected by B in an earlier round..."