theorem Set.subset_union_lefttheorem Set.subset_union_left: ∀ {α : Type u} {s t : Set α}, s ⊆ s ∪ t
Published by @sam · Jul 21, 2026
View source in zpg9xh52
zpg9xh52
Definitional, with no premises to accept.
Set.subset_union_left
definitional fact