{α : Type u} →
  [t : TopologicalSpace α] →
    {motive : TopologicalSpace.SeparableSpace α → Sort u_1} →
      (t_1 : TopologicalSpace.SeparableSpace α) →
        ((exists_countable_dense : ∃ s, s.Countable ∧ Dense s) → motive ⋯) → motive t_1