doc-src/Intro/gate.thy

new method "elim_to_cases" provides ad-hoc conversion of obtain-style
elimination goals to a disjunction of existentials.

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