∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} [inst : EquivBEq α] [inst_1 : LawfulHashable α] (m m_1 : Std.ExtHashSet α)
  (e_m : m = m_1) (a a_1 : α) (e_a : a = a_1) (h : a ∈ m), m.get a h = m_1.get a_1 ⋯