Theorem 19.23bi 747

Description: Inference from Theorem 19.23 of [Margaris] p. 90.

Hypothesis

Ref	Expression
19.23bi.1	⊢ (∃xφ → ψ)

Assertion

Ref	Expression
19.23bi	⊢ (φ → ψ)

Proof of Theorem 19.23bi

Step	Hyp	Ref	Expression
1		19.8a 712	. 2 ⊢ (φ → ∃xφ)
2		19.23bi.1	. 2 ⊢ (∃xφ → ψ)
3	1, 2	syl 12	1 ⊢ (φ → ψ)

Syntax hints:   → wi 2  ∃wex 678

This theorem is referenced by:  axreg 1083

This theorem was proved from axioms:  ax-1 3  ax-2 4  ax-3 5  ax-mp 6  ax-4 673

This theorem depends on definitions:  df-bi 128  df-ex 679

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