∀ {basis_hd : ℝ → ℝ} {basis_tl : ComputeAsymptotics.Basis} {exp : ℝ}
  {coef : ComputeAsymptotics.MultiseriesExpansion basis_tl}
  {tl : ComputeAsymptotics.MultiseriesExpansion.Multiseries basis_hd basis_tl}
  {x : ℝ × ComputeAsymptotics.MultiseriesExpansion basis_tl},
  x ∈ ComputeAsymptotics.MultiseriesExpansion.Multiseries.cons exp coef tl ↔ x = (exp, coef) ∨ x ∈ tl