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

State before:
α : Sort u_1
p : Prop
a : α
s t : Set α
⊢ (s.insertIf a p).union t = (Set.pureIf a p).union (s.union t)
Tactic:
rw [union_assoc]
State after:
no goals