Knaves alternately lie and tell the truth [TLT or LTL], and Liars can only lie.
Except when they are stricken with the Strange Averitas Flu Virus [SAFV]
and become sick. Strangely, as the name implies, when stricken with SAFV,
natives of every position behave differently: Knights behave as Knaves;
Knaves behave as Liars; and Liars behave as Knights.
Again, you are sent to KKL with a limited supply of the costly SAFV
To be certain none of the precious medicine is wasted, you must determine
which of the KKL natives are truly sick, and administer it only to them.
You interview a group of 6 KKL'ers, conveniently named A, B, C, D, E and F.
They are eager, if somewhat cryptic, in their attempts to advise you.
Their eighteen statements, in valid time sequence, follow:
A1. Anyone who, regardless of his state of health, can claim "I am sick" must be a Liar.
A2. B is not a sick Liar.
A3. I cannot claim to be a Liar who can tell the truth.
B1. I am not sick; but take that with a grain of salt, because I am also a Liar.
B2. D is a healthy Liar.
B3. I am a Knight.
C1. Everyone, on becoming sick, changes with regard to his ability to claim he is not a Knight. [edit for accuracy]
C2. Everyone, on becoming sick, must change his story about not being a Liar.
C3. Don't worry about me changing my story, though, I already need a shot.
D1. If a person who needs a shot claims that he is not a Liar, then he is indeed a Knight.
D2. It is only true of those persons who need a shot that the claim "I am not a Knave"
may be made by a person of any position.
D3. You can deduce that I, in fact, am not a Knave.
E1. Anyone who, regardless of his state of health, can claim "I am a Knight who can lie" must be a Knave.
E2. Collectively, the six of us are making equal numbers of true and false statements.
E3. Only one of us cannot claim not to be a Knave.
F1. Anyone who, regardless of his state of health, can claim to be a Knight must be a Knight.
F2. I am a Knave, and I really need a shot.
F3. There are at least two of us who have the same position and state of health.
To whom do you give shots?
Identify the Knights and Liars.