Question: What district was the successor seated in March 28, 1878?
SQL: SELECT "District" FROM "1-2417390-4" WHERE "Date successor seated" = 'March 28, 1878';

Question: Who was the vacator for the district of Nebraska At-large?
SQL: SELECT "Vacator" FROM "1-2417390-4" WHERE "District" = 'Nebraska At-large';