text: -- references to people in letters
  CREATE TABLE lookup_letters_refpersons (
    letter_id INT UNSIGNED NOT NULL,
    person_id INT UNSIGNED NOT NULL,
    direct_ref BOOLEAN,
    record_created_at TIMESTAMP DEFAULT NOW(),
    record_last_updated TIMESTAMP DEFAULT NOW(),
    FOREIGN KEY (letter_id) REFERENCES letters(id),
    FOREIGN KEY (person_id) REFERENCES persons(id),
    PRIMARY KEY (letter_id, person_id)
  ) ENGINE = innodb DEFAULT CHARSET = UTF8MB4 DEFAULT COLLATE = UTF8MB4_unicode_ci;
  