Thu, 08 Jan 2009 10:26:50 -0800 huffman add lemmas dvd_minus_iff and minus_dvd_iff in class comm_ring_1
Thu, 08 Jan 2009 10:07:39 -0800 huffman move lemmas mult_minus{left,right} inside class ring
Thu, 08 Jan 2009 09:58:36 -0800 huffman clean up division_ring proofs
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