Table schema:
CREATE TABLE table_name_78 (civil_liberties INTEGER, year VARCHAR, political_rights VARCHAR, president VARCHAR)

Question: When the president was Yoweri Museveni, and the year was 1993, with rank of 6 under political rights, what was the total of civil liberties?
SQL: SELECT SUM(civil_liberties) FROM table_name_78 WHERE political_rights = 6 AND president = "yoweri museveni" AND year = 1993