Clapp, F. L., & Huebner, B. P. (1924). The number combinations, their relative difficulty and the frequency of their appearance in text-books.
Lua i Stíl Chicago (17ú heag.)Clapp, Frank L., agus Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. Madison, Wis, 1924.
Lua MLA (8ú heag.)Clapp, Frank L., agus Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. 1924.
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