This is excellent, many thanks. Personally I'd got to McGuffin's fig 4 on the back of an envelope. Glad to find someone has taken things further. I'm plann

This is excellent, many thanks. Personally I'd got to McGuffin's fig 4 on the back of an envelope. Glad to find someone has taken things further. I'm planning on drawing an extensive family tree, it's surprising how much physical space they take up.