Columbia subject headings:
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.
Harvard subject headings:
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.
Princeton subject headings:
ʻUmar ibn al-Khaṭṭāb, Caliph, -644--Miscellanea.