CREATE TABLE table_78793 ("Date" TEXT, "Visitor" TEXT, "Score" TEXT, "Home" TEXT, "Record" TEXT)

Name the Visitor that has a Home of chicago black hawks on april 20?
SELECT "Visitor" FROM table_78793 WHERE "Home" = 'chicago black hawks' AND "Date" = 'april 20'
SELECT "Visitor" FROM "table_78793" WHERE "Date" = 'april 20' AND "Home" = 'chicago black hawks'