Katz, W. A. (2003). Digital reference services. Haworth Information Press.
Lua i Stíl Chicago (17ú heag.)Katz, William A. Digital Reference Services. Binghamton, N.Y: Haworth Information Press, 2003.
Lua MLA (9ú heag.)Katz, William A. Digital Reference Services. Haworth Information Press, 2003.
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