A number of economic concepts and techniques were applied in early Islamic banking, including bills of exchange, partnership ("mufawada", including limited partnerships, or "mudaraba"), and forms of capital ("al-mal"), capital accumulation ("nama al-mal"), cheques, promissory notes, trusts (see "Waqf"), Muslim traders are known to have used the cheque or "ṣakk" system since the time of Harun al-Rashid (9th century) of the Abbasid Caliphate. Organizational enterprises independent from the state also existed in the medieval Islamic world, while the agency institution was also introduced during that time. Many of these early capitalist concepts were adopted and further advanced in medieval Europe from the 13th century onwards.