Miller, R. L., & Ehrmann, E. (1979). Hummel: The complete collector's guide and illustrated reference / by Robert L. Miller and Eric Ehrmann (2. ed.). Portfolio Pr. Corp..
Lua i Stíl Chicago (17ú heag.)Miller, Robert L., agus Eric Ehrmann. Hummel: The Complete Collector's Guide and Illustrated Reference / by Robert L. Miller and Eric Ehrmann. 2. ed. Huntington, NY: Portfolio Pr. Corp., 1979.
Lua MLA (8ú heag.)Miller, Robert L., agus Eric Ehrmann. Hummel: The Complete Collector's Guide and Illustrated Reference / by Robert L. Miller and Eric Ehrmann. 2. ed. Portfolio Pr. Corp., 1979.
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