Talk:Disjunction elimination

It's been a while, but I seem to remember being taught that there was a second type of disjunction elimination:

A &or; B &not;A &there4; 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)

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