∀ (a : List UInt8) (isValidUTF8 : { data := { toList := a } }.IsValidUTF8),
  { toByteArray := { data := { toList := a } }, isValidUTF8 := isValidUTF8 } =
    { toByteArray := { data := { toList := a } }, isValidUTF8 := isValidUTF8 }