doc-src/Intro/gate.thy

partial_function (tailrec) replaces function (tailrec);
dropped unnecessary domain reasoning;
curried polydivide_aux

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