Which letter has an operator of VeriSign and an AS-number of AS26415?
CREATE TABLE "root_server_addresses" (
  "letter" text,
  "i_pv6_address" text,
  "as_number" text,
  "operator" text,
  "location_numsites_global_local" text,
  "software" text
);
SELECT "letter" FROM "root_server_addresses" WHERE "operator"='verisign' AND "as_number"='as26415';