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Wikipedia, the free encyclopedia.
\href{http://en.wikipedia.org/wiki/Cantor-Bernstein-Schroeder_theorem}
{http://en.wikipedia.org/wiki/Cantor-Bernstein-Schroeder\_theorem}.
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Wikipedia contributors.
Christian \protect{G}oldbach.
Wikipedia, the free encyclopedia.
\href{http://en.wikipedia.org/wiki/Goldbach}{http://en.wikipedia.org/wiki/Goldbach}.
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Wikipedia contributors.
Erdos number.
Wikipedia, the free encyclopedia.
\href{http://en.wikipedia.org/wiki/Erdos_number}{http://en.wikipedia.org/wiki/Erdos\_number}.
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Wikipedia contributors.
The four color theorem.
Wikipedia, the free encyclopedia.
\href{http://en.wikipedia.org/wiki/Four_color_theorem}{http://en.wikipedia.org/wiki/Four\_color\_theorem}.
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Leonard F.~Klosinski Gerald L.~Alexanderson and Loren~C. Larson.
\emph{The William Lowell Putnam Mathematical Competitions Problems & Solutions: 1965 - 1984}.
The Mathematical Association of America, Reissued 2003.
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Richard~K. Guy.
The lighthouse theorem, \protect{M}orley & \protect{M}alfatti -- a
budget of paradoxes.
\emph{American Mathematical Monthly}, 2007.
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Bjorn~Poonen Kiran S.~Kedlaya and Ravi Vakil.
\emph{The William Lowell Putnam Mathematical Competition 1985-2000:
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The Mathematical Association of America, 2002.
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C.~W.~H. Lam.
The search for a finite projective plane of order 10.
\href{http://www.cecm.sfu.ca/organics/papers/lam/paper/html/paper.html}{http://www.www.cecm.sfu.ca/organics/papers/lam/paper/html/paper.html}.
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Saunders MacLane.
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[12]
John~J. O'Connor and Edmund~F. Robertson.
\href{http://www-history.mcs.st-andrews.ac.uk/history/index.html}{http://www-history.mcs.st-andrews.ac.uk/history/index.html}.
The MacTutor History of Mathematics archive.
[13]
Stanislaw Radziszowski.
Small ramsey numbers.
\href{http://www.combinatorics.org/Surveys/ds1.pdf}
{http://www.combinatorics.org/Surveys/ds1.pdf}.
[14]
Gian-Carlo Rota.
\emph{Indiscrete Thoughts}.
Birkh\"{a}user, 1997.
[15]
M.~Satyanarayana.
none given.
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[16]
D.~J. Struik.
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Alfred~North Whitehead and Bertrand Russell.
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Cambridge University Press, 1910.