reverted e7a80c6752c9 -- there's not much point in putting a diagnosis tool (as opposed to a proof method) in Plain, but more importantly Sledgehammer must be in Main to use SMT solvers
Gate2 = FOL +
consts "~&" :: "[o,o] => o" (infixl 35)
"#" :: "[o,o] => o" (infixl 30)
If :: "[o,o,o] => o" ("if _ then _ else _")
rules nand_def "P ~& Q == ~(P & Q)"
xor_def "P # Q == P & ~Q | ~P & Q"
If_def "if P then Q else R == P&Q | ~P&R"
end