What's the network that has a callsign of XHTM and a D ERP of •?
CREATE TABLE "station_repeaters" (
  "callsign" text,
  "network" text,
  "city_of_license" text,
  "d_erp" text,
  "owner_operator" text
);
SELECT "network" FROM "station_repeaters" WHERE "d_erp"='•' AND "callsign"='xhtm';