Description: The Cartesian product of two finite sets is finite. (Contributed by Jeff Madsen, 2-Sep-2009) (Revised by Mario Carneiro, 12-Mar-2015) Avoid ax-pow . (Revised by BTernaryTau, 10-Jan-2025)
Ref | Expression | ||
---|---|---|---|
Assertion | xpfi | ⊢ ( ( 𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ) → ( 𝐴 × 𝐵 ) ∈ Fin ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | unfi | ⊢ ( ( 𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ) → ( 𝐴 ∪ 𝐵 ) ∈ Fin ) | |
2 | pwfi | ⊢ ( ( 𝐴 ∪ 𝐵 ) ∈ Fin ↔ 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ) | |
3 | pwfi | ⊢ ( 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ↔ 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ) | |
4 | 2 3 | bitri | ⊢ ( ( 𝐴 ∪ 𝐵 ) ∈ Fin ↔ 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ) |
5 | 1 4 | sylib | ⊢ ( ( 𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ) → 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ) |
6 | xpsspw | ⊢ ( 𝐴 × 𝐵 ) ⊆ 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) | |
7 | ssfi | ⊢ ( ( 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) ∈ Fin ∧ ( 𝐴 × 𝐵 ) ⊆ 𝒫 𝒫 ( 𝐴 ∪ 𝐵 ) ) → ( 𝐴 × 𝐵 ) ∈ Fin ) | |
8 | 5 6 7 | sylancl | ⊢ ( ( 𝐴 ∈ Fin ∧ 𝐵 ∈ Fin ) → ( 𝐴 × 𝐵 ) ∈ Fin ) |