Exercise 3.2  Answers
1 
(i)

It
shows that the argument is valid (assuming, of course, that you
have made no mistakes).


(ii) 
Nothing.
To conclude anything you need to go back to your interpretation
and, in the case of each open branch in the tableau, check whether
the unticked formulae are consistent, given what they mean. If there
is any open branch where the unticked formulae are consistent, the
argument is invalid. If in every case the unticked formulae are
inconsistent, the argument is valid.

2 
(i)

It shows
that the argument is valid (assuming, of course, that you have made
no mistakes).


(ii) 
Nothing.
To conclude anything you need to go back to your interpretation and
check each structure which provides a counterexample to see whether,
given what the sentenceletters mean, any of the structures are consistent
– i.e. represent a possibility. If any of the structures is
consistent, then the original argument is invalid. If they are all
inconsistent, the original argument is valid. 
