TODO

# Theory topics

- distinguish between sender (of a packet) and author (of a message)
- explain why we should hash ciphertext and/or (plaintext *and* a secret)
- explain that we assume message ID that can be calculated as soon as it is
  decrypted (for incoming messages) or encrypted (for outgoing messages). this
  doesn't hold true for mpCAT's "parent hashes", which can only be calculated
  after the message is echoed back from the server.

# Misc

- "sender" -> "author" in other places too

- move "tangents" (as pointed out by michael) to better places, maybe appendix

- It'd be easier to read if some typographic conventions are
  honoured in the writing. I'd suggest to use :math:``
  environments for all formulaic content as well as variable
  references. This would render variables (such as "u" and "a")
  usually in italics, and make reading much simpler.

- factor out the security/false-positive argument somewhere common
  - made twice in causal/02-consistency, once in appendix/05-hybrid

- categorise rules in 05-hybrid in a more systematic way