∀ (s sep : String),
  WellFounded
    (invImage
        (fun x =>
          PSigma.casesOn x fun b i =>
            PSigma.casesOn i fun i j =>
              PSigma.casesOn j fun j r => (s.rawEndPos.byteIdx - j.byteDistance i, sep.rawEndPos.byteIdx - j.byteIdx))
        Prod.instWellFoundedRelation).1