Theorem tb-ax2 34573

Description: The second of three axioms in the Tarski-Bernays axiom system. (Contributed by Anthony Hart, 16-Aug-2011.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
tb-ax2	⊢ (𝜑 → (𝜓 → 𝜑))

Proof of Theorem tb-ax2

Step	Hyp	Ref	Expression
1		ax-1 6	1 ⊢ (𝜑 → (𝜓 → 𝜑))

Syntax hints:   → wi 4

This theorem was proved from axioms:  ax-1 6

This theorem is referenced by:  re1ax2lem  34576