added !!!;
added is_semicolon;
export incr_line, keep_line, scan_blank, scan_string;
added source_proper;
added make_lexicon;
tuned;
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