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Metamath Proof Explorer
Description: Theorem *3.13 of WhiteheadRussell p. 111. (Contributed by NM, 3-Jan-2005)
|
|
Ref |
Expression |
|
Assertion |
pm3.13 |
⊢ ( ¬ ( 𝜑 ∧ 𝜓 ) → ( ¬ 𝜑 ∨ ¬ 𝜓 ) ) |
Proof
| Step |
Hyp |
Ref |
Expression |
| 1 |
|
pm3.11 |
⊢ ( ¬ ( ¬ 𝜑 ∨ ¬ 𝜓 ) → ( 𝜑 ∧ 𝜓 ) ) |
| 2 |
1
|
con1i |
⊢ ( ¬ ( 𝜑 ∧ 𝜓 ) → ( ¬ 𝜑 ∨ ¬ 𝜓 ) ) |