Mary, I don't think it's ever a good idea to impose books on a group.   (When I'm in a group where people are using RUS, I often won't open one even if it's there, and I'm not going to look at the book to sing a song I know by heart just because RUS may have altered the words or the chords.) But I really don't see why some people get bent out of shape because someone in the circle uses notes or a lyric sheet when it's their turn (scheduled or not) to sing a song. How is that "imposing" on the others?