Elshafei, A. (1968). Product Performance Models PPM. The Institute of National Planning.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रElshafei, Alwalid. Product Performance Models PPM. Cairo: The Institute of National Planning, 1968.
एमएलए (9वां संस्करण) प्रशस्ति पत्रElshafei, Alwalid. Product Performance Models PPM. The Institute of National Planning, 1968.
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