Some cases in "case ... of ..." expressions may now
be omitted (internally, these cases are assigned
the "undefined" value).
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