Theorem: Set.insert_idem (GMLInit/Data/Set/Insert.lean)

State before:
α : Sort u_1
a : α
s : Set α
⊢ (s.insert a).insert a = ((Set.pure a).union (Set.pure a)).union s
Tactic:
rw [union_assoc]
State after:
no goals

State before:
α : Sort u_1
a : α
s : Set α
⊢ ((Set.pure a).union (Set.pure a)).union s = (Set.pure a).union s
Tactic:
rw [union_idem]
State after:
no goals