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| Mirrors > Home > ILE Home > Th. List > eqeq12d | GIF version | ||
| Description: A useful inference for substituting definitions into an equality. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.) | 
| Ref | Expression | 
|---|---|
| eqeq12d.1 | ⊢ (𝜑 → 𝐴 = 𝐵) | 
| eqeq12d.2 | ⊢ (𝜑 → 𝐶 = 𝐷) | 
| Ref | Expression | 
|---|---|
| eqeq12d | ⊢ (𝜑 → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷)) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | eqeq12d.1 | . 2 ⊢ (𝜑 → 𝐴 = 𝐵) | |
| 2 | eqeq12d.2 | . 2 ⊢ (𝜑 → 𝐶 = 𝐷) | |
| 3 | eqeq12 2209 | . 2 ⊢ ((𝐴 = 𝐵 ∧ 𝐶 = 𝐷) → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷)) | |
| 4 | 1, 2, 3 | syl2anc 411 | 1 ⊢ (𝜑 → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷)) | 
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