removed obsolete theorems;
handle generic XML markup as well (plain <markup> instead of <... class=markup>);
misc tuning/update according to Pure/Generic/markup.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