Theorem pm2.86

Converse of Axiom [ax-2]. Theorem *2.86 of [WhiteheadRussell] p. 108. (Contributed by NM, 25-Apr-1994.) (Proof shortened by Wolf Lammen, 3-Apr-2013.)

Conclusion
\( \vdash ((\varphi \rightarrow \psi) \rightarrow \varphi \rightarrow \chi) \rightarrow \varphi \rightarrow \psi \rightarrow \chi \)
Proof
id
pm2.86d _