Theorem exbid

Formula-building rule for existential quantifier (deduction form). (Contributed by Mario Carneiro, 24-Sep-2016.)

Hypotheses
albid.1
\( \vdash \Finv x \, \varphi \)
albid.2
\( \vdash \varphi \rightarrow (\psi \leftrightarrow \chi) \)
Conclusion
\( \vdash \varphi \rightarrow (\exists x \, \psi \leftrightarrow \exists x \, \chi) \)
Proof
albid.1
l1
nf5ri _
albid.2
exbidh l1 _