Schaaf, W. L. (1969). Basic concepts of elementary mathematics. John Wiley and Sons.
Lua i Stíl Chicago (17ú heag.)Schaaf, William L. Basic Concepts of Elementary Mathematics. New York: John Wiley and Sons, 1969.
Lua MLA (9ú heag.)Schaaf, William L. Basic Concepts of Elementary Mathematics. John Wiley and Sons, 1969.
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