1. 1) K. Wakeyama, Let's Whistle (Kadokawa SS Comunications, Tokyo, 2007).
2. 2) K. Wakeyama, Practice with a World Champion! First Whistling Lesson (Doremi Music Publishing, Tokyo, 2014).
3. 3) M. Mori, "Science of a human whistling: How to whistle and the whistling certificate examination," J. Acoust. Soc. Jpn. (J), 67, 582–586 (2011) (in Japanese).
4. 4) M. Nilsson, J. S. Bartunek, J. Nordberg and I. Claesson, "Human whistle detection and frequency estimation," Proc. IEEE 2008 Congr. Image and Signal Processing, pp. 737–741 (2008).
5. 5) K. Harvest, "Theory of Whistling," https://youtu.be/JRP3jsZOZz4 (accessed 1 Dec. 2020).