CREATE TABLE table_1574968_1 (viewer VARCHAR2, language VARCHAR2)

Which viewers have the language of troff (typesetter runoff) , groff (gnu runoff)?
SELECT viewer FROM table_1574968_1 WHERE language = "troff (typesetter runoff) , groff (GNU runoff)"
SELECT "viewer" FROM "table_1574968_1" WHERE "language" = "troff (typesetter runoff) , groff (GNU runoff)"