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A Solution

  1. First determine and name the various propositions.

  2. We want to prove: $N \vee M$

  3. We are given:

  4. Sample Proof:
    1. $L \wedge \neg M \rightarrow N$, $N \rightarrow \neg M$, $L \Rightarrow N \vee M$

    2. $\neg (L \wedge \neg M) \vee N$, $\neg N \vee \neg M$, $L \Rightarrow N \vee M$ (R5)

    3. $\neg L \vee M \vee N$, $\neg N \vee \neg M$, $L \Rightarrow N \vee M$ (DeMorgan's)

    4. $\neg L \vee M \vee N$, $\neg N \vee \neg M$, $L \Rightarrow N$, $M$ (R2)

    5. Using R3 splits this sequent into 3 new sequents:
      $\neg L$, $\neg N \vee \neg M$, $L \Rightarrow N$, $M$ (R3 #1)
      $\neg N \vee \neg M$, $L \Rightarrow N$, $M$, $L$ (R1)
      This is a valid axiom by R6

    6. $M$, $\neg N \vee \neg M$, $L \Rightarrow N$, $M$ (R3 #2)
      This is a valid axiom by R6

    7. $N$, $\neg N \vee \neg M$, $L \Rightarrow N$, $M$ (R3 #3)
      This is a valid axiom by R6
All the sequents are resolved into valid axioms, so the proof by Wang's is completed.

Randy Latimer 2001-01-03