Description: The class of all ordinal numbers is its own union. Exercise 11 of TakeutiZaring p. 40. (Contributed by NM, 12-Nov-2003)
Ref | Expression | ||
---|---|---|---|
Assertion | unon | ⊢ ∪ On = On |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | eluni2 | ⊢ ( 𝑥 ∈ ∪ On ↔ ∃ 𝑦 ∈ On 𝑥 ∈ 𝑦 ) | |
2 | onelon | ⊢ ( ( 𝑦 ∈ On ∧ 𝑥 ∈ 𝑦 ) → 𝑥 ∈ On ) | |
3 | 2 | rexlimiva | ⊢ ( ∃ 𝑦 ∈ On 𝑥 ∈ 𝑦 → 𝑥 ∈ On ) |
4 | 1 3 | sylbi | ⊢ ( 𝑥 ∈ ∪ On → 𝑥 ∈ On ) |
5 | vex | ⊢ 𝑥 ∈ V | |
6 | 5 | sucid | ⊢ 𝑥 ∈ suc 𝑥 |
7 | suceloni | ⊢ ( 𝑥 ∈ On → suc 𝑥 ∈ On ) | |
8 | elunii | ⊢ ( ( 𝑥 ∈ suc 𝑥 ∧ suc 𝑥 ∈ On ) → 𝑥 ∈ ∪ On ) | |
9 | 6 7 8 | sylancr | ⊢ ( 𝑥 ∈ On → 𝑥 ∈ ∪ On ) |
10 | 4 9 | impbii | ⊢ ( 𝑥 ∈ ∪ On ↔ 𝑥 ∈ On ) |
11 | 10 | eqriv | ⊢ ∪ On = On |