Tue, 17 Oct 2000 10:27:28 +0200 paulson tidied some awkward proofs
Tue, 17 Oct 2000 10:26:07 +0200 paulson tidying; removed unused rev_contra_subsetD
Tue, 17 Oct 2000 10:23:16 +0200 paulson restoration of "equalityI"; renaming of contrapos rules
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