Comment #3 on issue 2412 by [email protected]: Sketch of Sister Celine's algorithm
http://code.google.com/p/sympy/issues/detail?id=2412

Is this still valid?  If so, where we should place this helper?

BTW, it seems, that every sum from this sketch could be evaluated with the current summation(). E.g.:
In [4]: summation((-1)**k*binomial(n,k)*binomial(2*n-2*k,n+a),(k,0,oo))
Out[4]:
⎧ ⎛ 2⋅n ⎞
⎪ ⎜     ⎟⋅Γ(-a)⋅Γ(-n + 1/2)
⎪ ⎝a + n⎠
⎪ ─────────────────────────    for re(a) < 0
⎪  ⎛  a   n⎞  ⎛  a   n   1⎞
⎪ Γ⎜- ─ - ─⎟⋅Γ⎜- ─ - ─ + ─⎟
⎪  ⎝  2   2⎠  ⎝  2   2   2⎠
⎪
⎪  ∞
⎨ ____
⎪ ╲
⎪  ╲       k ⎛n⎞ ⎛-2⋅k + 2⋅n⎞
⎪   ╲  (-1) ⋅⎜ ⎟⋅⎜          ⎟
⎪   ╱        ⎝k⎠ ⎝  a + n   ⎠    otherwise
⎪  ╱
⎪ ╱
⎪ ‾‾‾‾
⎪k = 0
⎩


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