Sun's curious identity

In combinatorics, Sun's curious identity is the following identity involving binomial coefficients, first established by Zhi-Wei Sun in 2002:

(x+m+1)\sum _{i=0}^{m}(-1)^{i}{\dbinom {x+y+i}{m-i}}{\dbinom {y+2i}{i}}-\sum _{i=0}^{m}{\dbinom {x+i}{m-i}}(-4)^{i}=(x-m){\dbinom {x}{m}}.

Proofs

After Sun's publication of this identity, five other proofs were obtained by various mathematicians:

Panholzer and Prodinger's proof via generating functions;
Merlini and Sprugnoli's proof using Riordan arrays;
Ekhad and Mohammed's proof by the WZ method;
Chu and Claudio's proof with the help of Jensen's formula;
Callan's combinatorial proof involving dominos and colorings.

gollark: I don't consider this clear because it's not distinguished from the *other* religious books which also claim to be ultimate universal truth.

gollark: I don't think this justifies being punished forever, *infinitely*, especially since, as you said, part of it is a product of the environment. Guess which omnipotent god set up that environment?

gollark: No, this is also terrible. They only punish you *after* you do things, with no clear guide about what's acceptable and what isn't.

gollark: I mean, sure, but other people will be eternally tortured.

gollark: I don't think they should be supporting entirely avoidable eternal torture.

References

Callan, D. (2004), "A combinatorial proof of Sun's 'curious' identity" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 4: A05, arXiv:math.CO/0401216.

Chu, W.; Claudio, L.V.D. (2003), "Jensen proof of a curious binomial identity" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 3: A20.

Ekhad, S. B.; Mohammed, M. (2003), "A WZ proof of a 'curious' identity" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 3: A06.

Merlini, D.; Sprugnoli, R. (2002), "A Riordan array proof of a curious identity" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 2: A08.

Panholzer, A.; Prodinger, H. (2002), "A generating functions proof of a curious identity" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 2: A06.

Sun, Zhi-Wei (2002), "A curious identity involving binomial coefficients" (PDF), INTEGERS: The Electronic Journal of Combinatorial Number Theory, 2: A04.

Sun, Zhi-Wei (2008), "On sums of binomial coefficients and their applications", Discrete Mathematics, 308 (18): 4231–4245, arXiv:math.NT/0404385, doi:10.1016/j.disc.2007.08.046.

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