Gae Bolga,
A ->B
A
therefore B is valid.
Another valid is
A->B
Not B
Therefore Not A.
What is invalid
is A->B
B
Therefore A.
As well
A->B
Not A
Therefore Not B.
The last two are invalid, and the first two are valid.
A ->B
A
therefore B is valid.
Another valid is
A->B
Not B
Therefore Not A.
What is invalid
is A->B
B
Therefore A.
As well
A->B
Not A
Therefore Not B.
The last two are invalid, and the first two are valid.