In that last example you might put a comma after b but never "and".
There is a wonderful book by Lynn Truss called Eats, Shoots and Leaves. Putting the comma after b is what lawyers would do.
I found a couple of links:
http://owl.english.purdue.edu/owl/resource/607/02/
http://grammar.about.com/od/punctuat...commaguide.htm
Hope they help.![]()
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