4017
Attendees at the  Istanbul  meeting included representatives of the 1920  Revolution Brigades  and the al-Rashideen Army which were among the Sunni insurgent groups formed to fight the U.S. occupation .
 city of headquarters: Istanbul, Revolution Brigades
Given options, please tell me the relationships of all the listed entity pairs.Output format is "relation1: word1, word2; relation2: word3, word4". 
Option: cities of residence, top members employees, members, alternate names, origin, state or provinces of residence, title of person, spouse, city of headquarters, NA, founded by, state or province of headquarters, employee of, countries of residence, country of birth, founded, subsidiaries, country of headquarters 
Text: {0} 
 Entity Pairs:  Istanbul, Revolution Brigades 
Answer:
 city of headquarters: Istanbul, Revolution Brigades