Semantic Consequence is Transitive
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Theorem
Let $\LL$ be a logical language.
Let $\mathscr M$ be a formal semantics for $\LL$.
Let $\FF, \GG$ and $\HH$ be sets of $\LL$-formulas.
Suppose that:
\(\ds \FF\) | \(\models_{\mathscr M}\) | \(\ds \GG\) | ||||||||||||
\(\ds \GG\) | \(\models_{\mathscr M}\) | \(\ds \HH\) |
Then $\FF \models_{\mathscr M} \HH$.
Proof
Let $\MM$ be an $\mathscr M$-structure.
By assumption, if $\MM$ is a model of $\FF$, it is one of $\GG$ as well.
But any model of $\GG$ is also a model of $\HH$.
In conclusion, any model of $\FF$ is also a model of $\HH$.
Hence the result, by definition of semantic consequence.
$\blacksquare$