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Metamath Proof Explorer

Theorem pm2.61d2

Description: Inference eliminating an antecedent. (Contributed by NM, 18-Aug-1993)

Ref Expression
Hypotheses pm2.61d2.1 ⊢ φ → ¬ ψ → χ
pm2.61d2.2 ⊢ ψ → χ
Assertion pm2.61d2 ⊢ φ → χ

Proof

Step Hyp Ref Expression
1 pm2.61d2.1 ⊢ φ → ¬ ψ → χ
2 pm2.61d2.2 ⊢ ψ → χ
3 2 a1i ⊢ φ → ψ → χ
4 3 1 pm2.61d ⊢ φ → χ