ˌɛni ɪnvˈɛɹiənt kwˈɔːɹɾɪk mˈʌst biː ˈiːvən ɪn bˈoʊθ ænd , ænd ɪnvˈɛɹiəns ˌʌndɚɹ ɛkstʃˈeɪndʒ ʌv koʊˈɔːɹdᵻnəts mˈiːnz ˌɛni ɪnvˈɛɹiənt kwˈɔːɹɾɪk kæn biː ɹˈɪʔn̩ dᵻspˈaɪt ðɪs bˌiːɪŋ ɐ tˈuːdᵻmˈɛnʃənəl vˈɛktɚ spˈeɪs, ðɪs kəntɹˈɪbjuːts ˈoʊnli wˈʌn nˈuː fˌʌndəmˈɛntəl ɪnvˈɛɹiənt æz lˈaɪz ɪnðə spˈeɪs.
Any invariant quartic must be even in both  and , and invariance under exchange of coordinates means any invariant quartic can be written  Despite this being a two-dimensional vector space, this contributes only one new fundamental invariant as  lies in the space.