Theorem con3th 924

Description: Contraposition. Theorem *2.16 of [WhiteheadRussell] p. 103. This version of con3 126 demonstrates the use of the weak deduction theorem dedt 923 to derive it from con3i 127. (Contributed by NM, 27-Jun-2002.) (Proof modification is discouraged.)

Assertion

Ref	Expression
con3th	⊢ ((φ → ψ) → (¬ ψ → ¬ φ))

Proof of Theorem con3th

Step	Hyp	Ref	Expression
1		id 19	. . . 4 ⊢ ((ψ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → (ψ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))))
2	1	notbid 285	. . 3 ⊢ ((ψ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → (¬ ψ ↔ ¬ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))))
3	2	imbi1d 308	. 2 ⊢ ((ψ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → ((¬ ψ → ¬ φ) ↔ (¬ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ))) → ¬ φ)))
4	1	imbi2d 307	. . . 4 ⊢ ((ψ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → ((φ → ψ) ↔ (φ → ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ))))))
5		id 19	. . . . 5 ⊢ ((φ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → (φ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))))
6	5	imbi2d 307	. . . 4 ⊢ ((φ ↔ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ)))) → ((φ → φ) ↔ (φ → ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ))))))
7		id 19	. . . 4 ⊢ (φ → φ)
8	4, 6, 7	elimh 922	. . 3 ⊢ (φ → ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ))))
9	8	con3i 127	. 2 ⊢ (¬ ((ψ ∧ (φ → ψ)) ∨ (φ ∧ ¬ (φ → ψ))) → ¬ φ)
10	3, 9	dedt 923	1 ⊢ ((φ → ψ) → (¬ ψ → ¬ φ))

This proof depends on syntax axioms:  ¬ wn 3   → wi 4   ↔ wb 176   ∨ wo 357   ∧ wa 358

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This proof depends on definitions:  df-bi 177  df-or 359  df-an 360

This theorem is used by: (None)