You're not supposed to spoil it. The whole point of these puzzles is the joy and knowledge you gets from solving them on your own. Publishing the answers is selfish.
Well, I for one don't consider this a satisfying solution (you could argue it does not count as a solution at all). How is the host supposed to evaluate the future? As I said in another comment, for that the host either needs iteration or an oracle, and both of those are missing from the premise of the question. It's like asking riddle where the solution is "Use a time-machine" when no time-machine is mentioned in the riddle: it's indicative of a riddle so weak it's almost an insult.
> How is the host supposed to evaluate the future?
I don't see how "evaluation of the future" is relevant. The person hosting the game has laid out the conditions for his actions. If you say "you will not give me prize B in response to this statement":
1) If the host were to give you prize B, that would be a contradiction, as that would make your statement false, so you should have received C.
2) If the host were to give you prize C, that would be a contradiction, as that would make your statement true; per the rules, you should not have received prize C (or logically equivalent: you should have received one of A or B).
3) If the host were to give you prize A, there is no contradiction.
The only action the host can make, while honoring the rules they laid out, is to give you prize A. The host, assuming they're decent at logic (which is a premise of such problems), would consider the above and realize that they must give you prize A. There's no need for reading the future; they must merely know what actions they are permitted to make given the rules of the game, and given only one valid course of action, they must take take that action.
I don't consider it a statement about the future but rather about the inevitable consequence whenever this game is played. Maybe it should be rephrased as: For this statement one will receive prize A or C.
@Carapace I find joy in discussing the validity of answers like this and such discussion is not possible without posting the answer first. I do feel sorry if I spoiled someone the joy of puzzling themselves though.
Yeah, I haven't quite got the hang of it myself. The encoding of formal logic in English sentences is fraught with ambiguity until you grok the specific style used.
Here's an example (SPOILER ALERT: with solution) of what I mean. The English version is just a verbose translation of a simple Boolean table.
==================================
Black-Hat Chuck
==================================
:date: 2014-02-01 10:56
:summary: A solution to the Three Hats puzzle.
I recently ran across a `cool puzzle site`_. Here is one of the puzzles
and a solution:
There are 3 black hats and 2 white hats in a box. Three men (we will
call them A, B, & C) each reach into the box and place one of the
hats on his own head. They cannot see what color hat they have
chosen. The men are situated in a way that A can see the hats on B &
C's heads, B can only see the hat on C's head and C cannot see any
hats. When A is asked if he knows the color of the hat he is wearing,
he says no. When B is asked if he knows the color of the hat he is
wearing he says no. When C is asked if he knows the color of the hat
he is wearing he says yes and he is correct. What color hat and how
can this be?
.. class:: attribution caption
~ `Three Hats`_
Solution
------------
I'm going to call the three men Alan, Bob, and Chuck.
First, let's imagine what Alan might be able to see. There are four
possibilities.
=========== =============
Bob's Hat Chuck's Hat
=========== =============
White White
Black White
White Black
Black Black
=========== =============
Since there are only two white hats, if Alan sees that both Bob's and
Chuck's hats are white his own hat would have to be black. In other
words, by admitting that he can't tell which hat he is wearing Alan is
saying that either or both of Bob's and Chuck's hats are black. If we
eliminate the case of both hats being white we are left with three
possibilities.
=========== =============
Bob's Hat Chuck's Hat
=========== =============
Black White
White Black
Black Black
=========== =============
From this it should be easy to see that if Bob sees that Chuck's hat is
white his own hat would have to be black. Bob would be uncertain of the
color of his own hat only if Chuck's hat is black. So Chuck, being no
dummy, can conclude that his own hat is black.
It's an elegant puzzle with a very simple and satisfying solution.
.. _cool puzzle site: http://wuriddles.com/
.. _Three Hats: http://wuriddles.com/easy.shtml#3hats
