Olson & Hajek (1999:112頁) Olson, Kenneth S; Hajek, John, The phonetic status of the labial flap, Journal of the International Phonetic Association, 1999, 29 (2): 101–114, doi:10.1017/S0025100300006484
Olson (2004:233頁) Olson, Kenneth S., Mono(PDF), Journal of the International Phonetic Association, 2004, 34 (02): 233–238 [2019-06-02], doi:10.1017/S0025100304001744, (原始内容存档(PDF)于2019-06-20)