Very timely question, Malcolm.

Yesterday I was speaking to a 'proper' musician (something I wouldn't call myself....a very enthusiastic amateur of long standing, me) about Joni Mitchell's song 'Both sides now' being difficult to sing. If the first part of the songs suits one's voice then the second part can be too high; likewise, if the second part suits then the first part is too low.

She used the word "inversion" and when I must have looked puzzled, she explained that it could make the song much easier to sing. I can see how that would happen.