import sqlite3


def list_db_vars(dbname):
    """
    Return the set of the names of the variables found in the specified case DB
    file.

    dbname: str
        The name of the sqlite DB file.
    """
    connection = sqlite3.connect(dbname)
    varcur = connection.cursor()
    varcur.execute("SELECT name from casevars")
    varnames = set([v for v in varcur])
    return varnames