Let [tex]\varphi[/tex] and [tex]\psi[/tex] both be formulae, and let [tex]\Gamma[/tex] be a set of formulae.(adsbygoogle = window.adsbygoogle || []).push({});

If [tex]\Gamma \cup \{\varphi\} \models \psi[/tex], then [tex]\Gamma \models (\varphi \rightarrow \psi)[/tex]

This is the principle by which the rule of inference known as Conditional Introduction is justified, but I cannot seem to find a proof for it, though the claim in the text is that it is an easy proof. Does anybody know what the proof is?

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# Proof of the Deduction Principle

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