Compound sum

• <mathtex>\sum^{(p)} = \underbrace{ \sum \circ \sum \circ \ldots \circ \sum }_{p-\text{times}}</mathtex>,
• <mathtex> \sum^{(0)} = id </mathtex>,
• <mathtex> \sum^{n,\,(p)}_{\alpha_{i+1}=1,\,(i)} = \underbrace{ \sum^{n}_{\alpha_2=1} \circ \sum^{n}_{\alpha_3=1} \circ \ldots \circ \sum^{n}_{\alpha_{p+1}=1} }_{p-\text{times}}</mathtex>,