nˈoʊɾɪs ðæt ðiːz ɛkspɹˈɛʃənz ɑːɹ ɚɹˈeɪndʒd sˌoʊ ðæt wiː nˈiːd tə kəmbˈaɪn ðə vˈɛɹiəs dˌiːˌɛftˈiː ˈaʊtpˌʊts baɪ pˈɛɹz ʌv ɐdˈɪʃənz ænd sʌbtɹˈækʃənz, wˌɪtʃ ɑːɹ nˈoʊn æz bˈʌɾɚflˌaɪz.
Notice that these expressions are arranged so that we need to combine the various DFT outputs by pairs of additions and subtractions, which are known as butterflies.