Columbia subject headings:
Shīʻah--Relations--Sunnites.
Sunnites--Relations--Shīʻah.
Harvard subject headings:
Shīʻites--Relations--Sunnites.
Sunnites--Relations--Shīʻites.
Princeton subject headings:
Shīʻah--Relations--Sunnites.
Sunnites--Relations--Shīʻah.