Theorem: Set.subset_union_left (GMLInit/Data/Set/Subset.lean)

State before:
α : Sort u_1
s✝ t✝ u s t : Set α
⊢ s.Subset (s.union t)
Tactic:
intro x hs
State after:
α : Sort u_1
s✝ t✝ u s t : Set α
x : α
hs : x ∈ s
⊢ x ∈ s.union t

State before:
α : Sort u_1
s✝ t✝ u s t : Set α
x : α
hs : x ∈ s
⊢ x ∈ s.union t
Tactic:
left
State after:
case h
α : Sort u_1
s✝ t✝ u s t : Set α
x : α
hs : x ∈ s
⊢ x ∈ s

State before:
case h
α : Sort u_1
s✝ t✝ u s t : Set α
x : α
hs : x ∈ s
⊢ x ∈ s
Tactic:
exact hs
State after:
no goals