"Iron and steel swords of China" (ISSC) is an excellent book containing many good examples of various antiques including the clipped tip chopper. There are several period manuals that list such weapons, and I think ISSC covers some of the ones I was thinking of.
For immediate gratification, this website has many useful pictures. (
http://thomaschen.freewebspace.com/catalog.html)
Go to the Song dynasty stuff to see a chopper that looks just like my Yi one.
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http://i77.photobucket.com/albums/j6...duation366.jpg)
I suspect that ergonomics and expediency have developed a similar chopping shape used as a farm implement and converted into a chopper in many regions. I have no idea what the origin of the wavy tip is, but it is also not uncommon in clipped tip pole arms.
Josh