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| Mirrors > Home > ILE Home > Th. List > nfan | GIF version | ||
| Description: If 𝑥 is not free in 𝜑 and 𝜓, it is not free in (𝜑 ∧ 𝜓). (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 13-Jan-2018.) | 
| Ref | Expression | 
|---|---|
| nfan.1 | ⊢ Ⅎ𝑥𝜑 | 
| nfan.2 | ⊢ Ⅎ𝑥𝜓 | 
| Ref | Expression | 
|---|---|
| nfan | ⊢ Ⅎ𝑥(𝜑 ∧ 𝜓) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | nfan.1 | . 2 ⊢ Ⅎ𝑥𝜑 | |
| 2 | nfan.2 | . . 3 ⊢ Ⅎ𝑥𝜓 | |
| 3 | 2 | a1i 9 | . 2 ⊢ (𝜑 → Ⅎ𝑥𝜓) | 
| 4 | 1, 3 | nfan1 1578 | 1 ⊢ Ⅎ𝑥(𝜑 ∧ 𝜓) | 
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