Description: Contraposition. Theorem *2.15 of WhiteheadRussell p. 102. Its associated inference is con1i . (Contributed by NM, 29-Dec-1992) (Proof shortened by Wolf Lammen, 12-Feb-2013)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | con1 | ⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ¬ 𝜓 → 𝜑 ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | id | ⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ¬ 𝜑 → 𝜓 ) ) | |
| 2 | 1 | con1d | ⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ¬ 𝜓 → 𝜑 ) ) |