This is to simplify matters...

I am particularly grateful for the patience of VideCorSpoon and Goapy. I enjoy philosophy but am having trouble getting my head around some of these logical matters.

So I need to show by sentence tableau that the sentence "[A v -A]" is a logical consequence of any sentence "R."

I believe we are dealing with "R -> [A v -A]" and while I don't know how to prove this by sentence tableau I think on a truth table it would appear like this:

A|R| R->[A v -A]
T|T T T T T FT
T|F F T T T FT
F|T T T F T TF
F|F F T F T T F

I think this shows by truth table that the sentence [A v-A] is a logical consequence of R, because under the "->" sign we have all T's. Now it's just to put it to sentence tableau. Am I ok so far?