NOR is Commutative/Proof 1
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Theorem
- $p \downarrow q \dashv \vdash q \downarrow p$
Proof
By the tableau method of natural deduction:
Line | Pool | Formula | Rule | Depends upon | Notes | |
---|---|---|---|---|---|---|
1 | 1 | $p \downarrow q$ | Premise | (None) | ||
2 | 1 | $\neg \paren {p \lor q}$ | Sequent Introduction | 1 | Definition of Logical NOR | |
3 | 1 | $\neg \paren {q \lor p}$ | Sequent Introduction | 2 | Disjunction is Commutative | |
4 | 1 | $q \uparrow p$ | Sequent Introduction | 3 | Definition of Logical NOR |
$\Box$
By the tableau method of natural deduction:
Line | Pool | Formula | Rule | Depends upon | Notes | |
---|---|---|---|---|---|---|
1 | 1 | $q \downarrow p$ | Premise | (None) | ||
2 | 1 | $\neg \paren {q \lor p}$ | Sequent Introduction | 1 | Definition of Logical NOR | |
3 | 1 | $\neg \paren {p \lor q}$ | Sequent Introduction | 2 | Disjunction is Commutative | |
4 | 1 | $p \downarrow q$ | Sequent Introduction | 3 | Definition of Logical NOR |
$\blacksquare$