 Luigi Guido Grandi

Luigi Guido Grandi was a mathematician and monk whose work included geometry and hydraulics. His name is associated with Grandi's series, $1-1+1-1+\cdots$, a simple example that exposes ambiguities in manipulating infinite sums.^[ref] Grouping consecutive terms as $(1-1)+(1-1)+\cdots$ suggests zero, while separating the first term suggests one; neither is a valid proof of an ordinary sum. The partial sums do not converge. A specified method such as Cesàro summation can assign $1/2$, but the method and its rules must be stated before using that value in a calculation.