Definition:Constructed Semantics/Instance 3/Rule of Commutation
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Theorem
The Rule of Commutation:
- $\left({p \lor q}\right) \implies \left({q \lor p}\right)$
is a tautology in Instance 3 of constructed semantics.
Proof
By the definitional abbreviation for the conditional:
- $\mathbf A \implies \mathbf B =_{\text{def}} \neg \mathbf A \lor \mathbf B$
the Rule of Commutation can be written as:
- $\neg \left({p \lor q}\right) \lor \left({q \lor p}\right)$
This evaluates as follows:
- $\begin{array}{|cccc|c|ccc|} \hline
\neg & (p & \lor & q) & \lor & (q & \lor & p) \\ \hline 2 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 2 & 0 & 0 & 1 & 0 & 1 & 0 & 0 \\ 2 & 0 & 0 & 2 & 0 & 2 & 0 & 0 \\ 2 & 1 & 0 & 0 & 0 & 0 & 0 & 1 \\ 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\ 0 & 1 & 2 & 2 & 0 & 2 & 2 & 1 \\ 2 & 2 & 0 & 0 & 0 & 0 & 0 & 2 \\ 0 & 2 & 2 & 1 & 0 & 1 & 2 & 2 \\ 0 & 2 & 2 & 2 & 0 & 2 & 2 & 2 \\ \hline \end{array}$
$\blacksquare$