∀ {basis : Tactic.ComputeAsymptotics.Basis} {f : ℝ → ℝ} {ex_tl : Tactic.ComputeAsymptotics.BasisExtension basis},
  Tactic.ComputeAsymptotics.WellFormedBasis (Tactic.ComputeAsymptotics.BasisExtension.insert f ex_tl).getBasis →
    Tactic.ComputeAsymptotics.WellFormedBasis ex_tl.getBasis