{P : Sort u} →
  {toNormal toSpecial toNormal' toSpecial' : Std.HashMap Char Char} →
    { toNormal := toNormal, toSpecial := toSpecial } = { toNormal := toNormal', toSpecial := toSpecial' } →
      (toNormal = toNormal' → toSpecial = toSpecial' → P) → P