Lower fixed binomial coefficient → overlapping combination

$\left(\genfrac{}{}{0ex}{}{A+i}{A}\right)=\left(\genfrac{}{}{0ex}{}{A+i}{i}\right)=H_i^{A+1}$

$\left(\genfrac{}{}{0ex}{}{A+i}{A}\right)=H_A^{i+1}$ The latter is also possible, but the former is a more natural form of Collapsing Duplicate Combinations since it is a form of placing a variable ball on a fixed frame.

• binomial coefficient of under-fixation → nested combination

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