Não informado. Publications of the Allegheny Observatory of the University of Pittsburgh. University of Pittsburgh.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Publications of the Allegheny Observatory of the University of Pittsburgh. Lancaster, Pa: University of Pittsburgh.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Publications of the Allegheny Observatory of the University of Pittsburgh. University of Pittsburgh.
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