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$f(m,n)=\binom{m}{m}\binom{n}{1}+\binom{m}{m-1}\binom{n}{2}+\cdots+\binom{m}{2}\binom{n}{m-1}+\binom{m}{1}\binom{n}{m}=?$

Can we simplify the expression above?

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    $\begingroup$ This type of expression is very well known. See Concrete Mathematics by Graham, Knuth, and Patashnik, particularly table 174 (p. 174). $\endgroup$
    – Todd Trimble
    Oct 2, 2010 at 0:21
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    $\begingroup$ (I should have paused; this looks like homework.) $\endgroup$
    – Todd Trimble
    Oct 2, 2010 at 0:23
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    $\begingroup$ en.wikipedia.org/wiki/Chu-Vandermonde_identity $\endgroup$ Oct 2, 2010 at 6:25

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