Prove that if for some formulae A and B it is the case that j=taut A ! B and B j=taut ?

Prove that if for some formulae A and B it is the case that

> j=taut A ! B and B j=taut ?, then it is also the case that j=taut :A.

Here, using truth tables or truth-table tricks, you will show that if you

have the left side of the then" in the statement, then you must have the

right side as well.