: <math> f_1(x) = \operatorname{rect} \left( \frac{x}{\Delta x} \right) \otimes \sum_{i} \delta (x - \Delta xi) \cdot (-1)^i </math> | : <math> f_1(x) = \operatorname{rect} \left( \frac{x}{\Delta x} \right) \otimes \sum_{i} \delta (x - \Delta xi) \cdot (-1)^i </math> |