A binary function that takes a pair of space regions (see homogeneous positive dimensional space region) of the same dimensionality (see Spatially Equidimensional) to their symmetric difference . (Symmetric Space Region Difference Fn SYMDIFF REGION1 REGION2) means that SYMDIFF is the mereological difference (see Space Region Difference) between the sum (see Space Region Sum) of REGION1 and REGION2 and the product (see Space Region Product) of REGION1 and REGION2.

Currently, this function is an EL relation whose Expansion given in terms of Space Region Difference, Space Region Product Fn, and Space Region Sum Fn.

See also the corresponding predicate symmetric spatial difference of.