∀ {α : Type u} {β : Type v} {x : BEq α} {x_1 : Hashable α} {m₁ m₂ : Std.ExtHashMap α β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] {k : α} {h_mem : k ∈ m₁ ∩ m₂}, (m₁ ∩ m₂).get k h_mem = m₁.get k ⋯