CREATE TABLE table_12683 ("Year" FLOAT, "Award Ceremony" TEXT, "Category" TEXT, "Nominee" TEXT, "Result" TEXT)

Which Nominee has an Award Ceremony of tony award, and a Category of the best performance by a leading actor in a musical?
SELECT "Nominee" FROM table_12683 WHERE "Award Ceremony" = 'tony award' AND "Category" = 'best performance by a leading actor in a musical'
SELECT "Nominee" FROM "table_12683" WHERE "Award Ceremony" = 'tony award' AND "Category" = 'best performance by a leading actor in a musical'