theory (Or "smash sum") In domain theory, the coalesced sum of domains A and B, A (+) B, contains all the non-bottom elements of both domains, tagged to show which part of the sum they come from, and a new bottom element. D (+) E = bottom(D(+)E) U (0,d) | d in D, d /= bottom(D) U (1,e) | e in E, e /= bottom(E) The bottoms of the constituent domains are coalesced into a single bottom in the sum. This may be generalised to any number of domains. The ordering is bottom(D(+)E) (i,v1) "LaTeX \sqsubseteq and "(+)" as LaTeX \oplus - a "+" in a circle. (1994-12-22)