$(6$ MARKS$)$ Recall that a schema is a tautology iff all its instances are

tautologies.

Which of the following six schemata are tautologies? Show the whole

process that led to your answers, including truth tables or equivalent short

cuts, if you used one or the other, and words of explanation if needed.

I note that in the six sub$-$questions below I am $$ using all the

formally necessary brackets. You need to reinsert missing brackets to an$-$

swer correctly.

$AB-=$notAvvB

$((AB)C)-=(A(BC))$

$A^{{?}^{?}}B-=$not$(notAvvnotB)$

$ABC-=BAC$

$AB-=$notB$$notA

$((AB)A)A$