Elshafei, A. (1968). Product Performance Models PPM. The Institute of National Planning.
Chicago-čujuhus (17. p.)Elshafei, Alwalid. Product Performance Models PPM. Cairo: The Institute of National Planning, 1968.
MLA-čujuhus (9. p.)Elshafei, Alwalid. Product Performance Models PPM. The Institute of National Planning, 1968.
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