uniform treatment of ML indexing, using general \indexdef macro for formal Isabelle/Isar entities;
more robust handling of "|" within index;
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