Consider the following (well known)
problem:
A
convict heard the
judge's
veredict:
"for your
crimes, you shall be executed one day of the coming week. You can not know which day you shall be executed until
noon of that same day"
in short we have
- a convict shall be executed in one of the next 7 days (he know this)
- he must not know which day he shall be executed
until that day arrives
The
convict upon hearing the
sentence placed the following
argument:
I know then that I shall not be executed on the seventh day, for if I were alive I would know that I would have to be executed on that day (thus failing II).
We have eliminated day 7 as a possible execution date so we have 6 days remaining for it.
If the morning of the sixth day comes, I would know that I would have to be executed that day (since number 7 has already been eliminated) and, for II) to be true , I cannot be executed on the sixth day.
I can make the same argument for days 5, 4, 3, 2, 1, and as such I can never be executed based on that
sentence for it would violate II). But if I'm not executed, it'll violate I).
The
judge didn't listen, and the
convict was executed in the afternoon of day 4. Both I) and II) were
true.
This is the
element of surprise.