Treats the grid as a grid of one- dimensional grids such that the same operation (here addition) will be performed on all its elements together with the base value. the results are combined back. each #fold operation removes a dimension. syntax: #fold some other forms: [#fold +] computes totals [#fold inv+] is an alternated sum (+/-) [#fold *] can compute the size of a grid using its dimension list [#fold &] can mean "for all" [#fold |] can mean "there exists (at least one)" [#fold ^] can mean "there exists an odd number of..." the operator to fold with. Outputs a grid that has one less dimension than the input. the initial value for the folding. (default: none) this can be a grid of any size, and this decides the size of the subgrids we are working on: a seed that has N dimensions will cause the folding to happen on the dimension that is just before the last N dimensions. replaces every subgrid (of one or more dimensions) by the result of a cascade on that subgrid. Doing that with seed value 0 and operation + on grid "2 3 5 7" will compute ((((0+2)+3)+5)+7) find the total "17".