Theorem
orim2
Axiom *1.6 (Sum) of [WhiteheadRussell] p. 97. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash (\psi \rightarrow \chi) \rightarrow \varphi \vee \psi \rightarrow \varphi \vee \chi \)
Proof
id
orim2d
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