Theorem rb-ax2 1759

Description: The second of four axioms in the Russell-Bernays axiom system. (Contributed by Anthony Hart, 13-Aug-2011.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
rb-ax2	⊢ (¬ (𝜑 ∨ 𝜓) ∨ (𝜓 ∨ 𝜑))

Proof of Theorem rb-ax2

Step	Hyp	Ref	Expression
1		pm1.4 865	. . . 4 ⊢ ((𝜑 ∨ 𝜓) → (𝜓 ∨ 𝜑))
2	1	con3i 154	. . 3 ⊢ (¬ (𝜓 ∨ 𝜑) → ¬ (𝜑 ∨ 𝜓))
3	2	con1i 147	. 2 ⊢ (¬ ¬ (𝜑 ∨ 𝜓) → (𝜓 ∨ 𝜑))
4	3	orri 858	1 ⊢ (¬ (𝜑 ∨ 𝜓) ∨ (𝜓 ∨ 𝜑))

Syntax hints:  ¬ wn 3   ∨ wo 843

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 206  df-or 844

This theorem is referenced by:  rblem1  1763  rblem2  1764  rblem3  1765  rblem4  1766  rblem5  1767  rblem6  1768  re2luk1  1771  re2luk2  1772  re2luk3  1773