MacTutor
Σ ± was Cauchy's notation for the determinant (1812).
(Σ ±) (a e k) represented the determinant
where the non-diagonal elements were filled appropriately.
(Σ ±) (a e k) represented the determinant
where the non-diagonal elements were filled appropriately.
The determinant Qp in the paper is the (n+1) × (n+1) determinant 
.