# Exclusive Or with Tautology/Proof 1

## Theorem

$p \oplus \top \dashv \vdash \neg p$

## Proof

By the tableau method of natural deduction:

$p \oplus \top \vdash \neg p$
Line Pool Formula Rule Depends upon Notes
1 1 $p \oplus \top$ Premise (None)
2 1 $\left({p \lor \top} \right) \land \neg \left({p \land \top}\right)$ Sequent Introduction 1 Definition of Exclusive Or
3 1 $\top \land \neg \left({p \land \top}\right)$ Sequent Introduction 1 Disjunction with Tautology
4 1 $\neg \left({p \land \top}\right)$ Sequent Introduction 1 Conjunction with Tautology
5 1 $\neg p$ Sequent Introduction 1 Conjunction with Tautology

$\Box$

By the tableau method of natural deduction:

$\neg p \vdash p \oplus \top$
Line Pool Formula Rule Depends upon Notes
1 1 $\neg p$ Assumption (None)
2 $\top$ Rule of Top-Introduction: $\top \mathcal I$ (None)
3 $p \lor \top$ Sequent Introduction 2 Disjunction with Tautology
4 1 $\neg \left({p \land \top}\right)$ Sequent Introduction 1 Conjunction with Tautology
5 1 $\left({p \lor \top}\right) \land \neg \left({p \land \top}\right)$ Rule of Conjunction: $\land \mathcal I$ 3, 4
6 1 $p \oplus \top$ Sequent Introduction 5 Definition of Exclusive Or

$\blacksquare$