moved theorem tags from Drule to PureThy;
replaced kind attribute by kind string;
tuned name_multi: index > 1 only;
added note_thmss_qualified (from Isar/locale.ML);
Gate = FOL +
consts nand,xor :: "[o,o] => o"
rules nand_def "nand(P,Q) == ~(P & Q)"
xor_def "xor(P,Q) == P & ~Q | ~P & Q"
end