1 \documentstyle[12pt
]{article
}
6 q_i & = &
\sum_{j=i_1
}^
{i_N
} \eta_{ji
}\left(r_
{ij
}\right) \\
7 \sigma_i & = &
\sum_{j=i_1
}^
{i_N
} q_j
\cdot \psi_{ij
} \left(r_
{ij
}\right) \\
8 E_i
\left(q_i,
\sigma_i\right) & = &
\frac{1}{2} \cdot q_i
\cdot \sigma_i