Now I have a bit of work reviewing all the comments, suggestions and Matias' replies to write an small summary of requested changes and conclusions. The "relation" view, and some basic names ("first"/"second" vs. "left"/"right") were the most active topics. But everyone has considered Bimap useful, well-written, and well documented. I'll post the summary following week.
My vote (?) would be to keep left and right - seemed pretty intuitive to me on reading. Didn't have time to review or use library, but impressed with overall thought and documentation effort (which I did read!) James This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. Any unauthorized disclosure, copying, distribution or reliance on the contents of this information is strictly prohibited and may constitute a violation of law. If you are not the intended recipient, please notify the sender immediately by responding to this e-mail, and delete the message from your system. If you have any questions about this e-mail please notify the sender immediately.