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| Mirrors > Home > ILE Home > Th. List > lencl | GIF version | ||
| Description: The length of a word is a nonnegative integer. This corresponds to the definition in Section 9.1 of [AhoHopUll] p. 318. (Contributed by Stefan O'Rear, 27-Aug-2015.) |
| Ref | Expression |
|---|---|
| lencl | ⊢ (𝑊 ∈ Word 𝑆 → (♯‘𝑊) ∈ ℕ0) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | iswrd 11162 | . . 3 ⊢ (𝑊 ∈ Word 𝑆 ↔ ∃𝑙 ∈ ℕ0 𝑊:(0..^𝑙)⟶𝑆) | |
| 2 | 1 | biimpi 120 | . 2 ⊢ (𝑊 ∈ Word 𝑆 → ∃𝑙 ∈ ℕ0 𝑊:(0..^𝑙)⟶𝑆) |
| 3 | fnfzo0hash 11143 | . . . 4 ⊢ ((𝑙 ∈ ℕ0 ∧ 𝑊:(0..^𝑙)⟶𝑆) → (♯‘𝑊) = 𝑙) | |
| 4 | 3 | adantl 277 | . . 3 ⊢ ((𝑊 ∈ Word 𝑆 ∧ (𝑙 ∈ ℕ0 ∧ 𝑊:(0..^𝑙)⟶𝑆)) → (♯‘𝑊) = 𝑙) |
| 5 | simprl 531 | . . 3 ⊢ ((𝑊 ∈ Word 𝑆 ∧ (𝑙 ∈ ℕ0 ∧ 𝑊:(0..^𝑙)⟶𝑆)) → 𝑙 ∈ ℕ0) | |
| 6 | 4, 5 | eqeltrd 2308 | . 2 ⊢ ((𝑊 ∈ Word 𝑆 ∧ (𝑙 ∈ ℕ0 ∧ 𝑊:(0..^𝑙)⟶𝑆)) → (♯‘𝑊) ∈ ℕ0) |
| 7 | 2, 6 | rexlimddv 2656 | 1 ⊢ (𝑊 ∈ Word 𝑆 → (♯‘𝑊) ∈ ℕ0) |
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