Theorem qexmid 796

Description: Quantified "excluded middle". Exercise 9.2a of Boolos, p. 111, Computability and Logic.

Assertion

Ref	Expression
qexmid	⊢ ∃x(φ → ∀xφ)

Proof of Theorem qexmid

Step	Hyp	Ref	Expression
1		19.8a 712	. 2 ⊢ (∀xφ → ∃x∀xφ)
2	1	19.35ri 756	1 ⊢ ∃x(φ → ∀xφ)

Syntax hints:   → wi 2  ∀wal 672  ∃wex 678

This theorem was proved from axioms:  ax-1 3  ax-2 4  ax-3 5  ax-mp 6  ax-4 673  ax-5 674  ax-gen 677

This theorem depends on definitions:  df-bi 128  df-an 198  df-ex 679

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