What is the Gecko value for the item that has a Prince XML value of 'no' and a KHTML value of 'yes'?
CREATE TABLE "grammar_and_rules" (
  "trident" text,
  "gecko" text,
  "web_kit" text,
  "khtml" text,
  "presto" text,
  "prince_xml" text
);
SELECT "gecko" FROM "grammar_and_rules" WHERE "prince_xml"='yes' AND "khtml"='yes';