Talk:Disjunction elimination
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It's been a while, but I seem to remember being taught that there was a second type of disjunction elimination:
A ∨ B ¬A ∴ B
It's obviously logically valid. Does it have a different name? I can't find it listed on propositional calculus. Evercat 00:07 18 Jun 2003 (UTC)
While I'm at it, does this look like a valid derivation of the above? It's been a while since I've done a derivation...
1 1 P v Q A 2 2 -P A 3 3 P A (for v-E) 4 4 -Q A (for RAA) 2,3 5 P & -P &-I 2,3 2,3,4 6 (P & -P) & -Q &-I 4,5 2,3,4 7 P & -P &-E 6 2,3 8 --Q RAA 7,4 2,3 9 Q DNE 8 10 10 Q A (for v-E) 1,2 11 Q v-E 1,3,9,10,10
I worked this out myself. :-)
Still, looking at my notes I can't actually find this as a 2nd type of or-elimination, so I'll just leave this lying in the talk page for now... Evercat 16:56 21 Jun 2003 (UTC)