Description: A class equinumerous to a successor is never empty. (Contributed by RP, 11-Nov-2023) (Proof shortened by SN, 16-Nov-2023)
Ref | Expression | ||
---|---|---|---|
Assertion | ensucne0 | ⊢ ( 𝐴 ≈ suc 𝐵 → 𝐴 ≠ ∅ ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nsuceq0 | ⊢ suc 𝐵 ≠ ∅ | |
2 | ensymb | ⊢ ( ∅ ≈ suc 𝐵 ↔ suc 𝐵 ≈ ∅ ) | |
3 | en0 | ⊢ ( suc 𝐵 ≈ ∅ ↔ suc 𝐵 = ∅ ) | |
4 | 2 3 | bitri | ⊢ ( ∅ ≈ suc 𝐵 ↔ suc 𝐵 = ∅ ) |
5 | 1 4 | nemtbir | ⊢ ¬ ∅ ≈ suc 𝐵 |
6 | breq1 | ⊢ ( 𝐴 = ∅ → ( 𝐴 ≈ suc 𝐵 ↔ ∅ ≈ suc 𝐵 ) ) | |
7 | 5 6 | mtbiri | ⊢ ( 𝐴 = ∅ → ¬ 𝐴 ≈ suc 𝐵 ) |
8 | 7 | necon2ai | ⊢ ( 𝐴 ≈ suc 𝐵 → 𝐴 ≠ ∅ ) |