[ADVANCED\]XY_SHORT [Arg] Compute the Short Spacings image from the current "Single Dish" dataset (read by READ SINGLE) when this dataset is a Class table, and make it avail- able as the SHORT image variable. If the "Single Dish" dataset is already a 3-D data cube, nothing is done as it is alreay accessible through the SHORT image variable. XY_SHORT uses the same input parameters as UV_SHORT. It corresponds to Step_1 of UV_SHORT.