Vrat, P., & Sardana, G. S. (1998). Productivity management: A system approach. Narosa Publishing House.
Lua i Stíl Chicago (17ú heag.)Vrat, Prem, agus G.D. Sahay Sardana. Productivity Management: A System Approach. New Delhi: Narosa Publishing House, 1998.
Lua MLA (8ú heag.)Vrat, Prem, agus G.D. Sahay Sardana. Productivity Management: A System Approach. Narosa Publishing House, 1998.
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