Pure/library/enclose, Pure/Syntax/pretty/enclose: renamed from parents
Pure/library/is_blank: now handles form feeds () too, in accordance with
ML definition
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