[jblezo]

I agree for A), by why D) ?

[chias]

I suspect a misreading of D) as "The liar has at least one non-green hat" which, in fairness, feels weird that wasn't included in the list.

[autokad]

I did that myself, not sure whats wrong with my eyes >.<

[jblezo]

Also, I'm not sure that those two affirmations are equivalent:

  ~∀x  (~IsAHatOfMine(x) ∨  Green(x))

   ∃x ~(~IsAHatOfMine(x) ∨  Green(x))

[FabHK]

That's basically "infinite" DeMorgan:

https://en.wikipedia.org/wiki/De_Morgan's_laws#Extension_to_...