Theorem pm2.67 231

Description: Theorem *2.67 of [WhiteheadRussell] p. 107.

Assertion

Ref	Expression
pm2.67	⊢ (((φ ∨ ψ) → ψ) → (φ → ψ))

Proof of Theorem pm2.67

Step	Hyp	Ref	Expression
1		orc 225	. 2 ⊢ (φ → (φ ∨ ψ))
2	1	syl4 19	1 ⊢ (((φ ∨ ψ) → ψ) → (φ → ψ))

Syntax hints:   → wi 2   ∨ wo 195

This theorem is referenced by:  pm4.72 485

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

This theorem depends on definitions:  df-bi 128  df-or 197

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