Columbia subject headings:
Caliphs--Islamic Empire--Biography.
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.
Harvard subject headings:
Caliphs--Biography
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.
Princeton subject headings:
Caliphs--Biography.
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.