A colleague of mine has posed a question with which I am struggling. Perhaps you can help.
Here is the question: "Can you think of an example [in the history of mathematics] in which mathematicians have changed a classification system? It would be as though first surfaces were characterized by type of fiber (in certain fibrations) and then decades later by Kodaira dimension. Or as though the first categories into which we separate groups weren't always abelian/nonabelian. I'm looking for something where there were object-types, let's call them a b c d e f g h i j, and they were once grouped by characteristic A so that they fell into (a b c) (d e) (f g h i j)... later it was thought that characteristic B was more important, so they were now thought of as (a d g h) (b c j) (e f i). I'm not sure this has ever happened, which is why I'm asking."
Daniel E. Otero Dept. of Mathematics & Computer Science Xavier University Cincinnati, OH 45207-4441 513-745-2012