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 mereological difference in the sense of Region Connection Calculus 8 Theory. (Space Region Difference Fn REG1 REG2) is the product (see Space Region Product Fn) of REG1 and the complement (see Space Region Complement Fn) of REG2.

See the corresponding predicate Space Region Difference. Also see Space Region Sum Fn.

Note that Space Region Difference Fn is the function called diff in the paper on spatial logic by Randell, Cui, and Cohn (1992).