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Metamath Proof Explorer
Description: Theorem *2.73 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005)
|
|
Ref |
Expression |
|
Assertion |
pm2.73 |
⊢ ( ( 𝜑 → 𝜓 ) → ( ( ( 𝜑 ∨ 𝜓 ) ∨ 𝜒 ) → ( 𝜓 ∨ 𝜒 ) ) ) |
Proof
| Step |
Hyp |
Ref |
Expression |
| 1 |
|
pm2.621 |
⊢ ( ( 𝜑 → 𝜓 ) → ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) ) |
| 2 |
1
|
orim1d |
⊢ ( ( 𝜑 → 𝜓 ) → ( ( ( 𝜑 ∨ 𝜓 ) ∨ 𝜒 ) → ( 𝜓 ∨ 𝜒 ) ) ) |