A way of figuring out the size of the dimensions in an array, other than getting an error when you don't use the right size (e.g. LOAD"DAT:2DARRAY",ARRAY may result in LEN(ARRAY) being 12; the array might be [1,12], [2,6], [3,4], [4,3], [6,2], or [12,1], and there's no way of knowing except getting errors for using indices that are out-of-bounds).