Description: Subclass relationship for union of classes. (Contributed by NM, 30-Aug-1993)
Ref | Expression | ||
---|---|---|---|
Assertion | ssun2 | ⊢ 𝐴 ⊆ ( 𝐵 ∪ 𝐴 ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ssun1 | ⊢ 𝐴 ⊆ ( 𝐴 ∪ 𝐵 ) | |
2 | uncom | ⊢ ( 𝐴 ∪ 𝐵 ) = ( 𝐵 ∪ 𝐴 ) | |
3 | 1 2 | sseqtri | ⊢ 𝐴 ⊆ ( 𝐵 ∪ 𝐴 ) |