∀ {K : Type u_2} {L : Type u_3} [inst : Field K] [inst_1 : Field L] [inst_2 : Algebra K L]
  [inst_3 : IsPurelyInseparable K L] {a : L} {n : ℕ},
  a ^ ringExpChar K ^ n ∈ (algebraMap K L).range → IsPurelyInseparable.elemExponent K a ≤ n