1. < theory > In domain theory , the sum A + B of two domain s contains all elements of both domains, modified to indicate which part of the union they come from, plus a new bottom element. There are two constructor functions associated with the sum:
inA : A -> A+B inB : B -> A+B inA(a) = (0,a) inB(b) = (1,b)
and a disassembly operation:
case d of E1; isB(x) -> E2">isA(x) -> E1; isB(x) -> E2
This can be generalised to arbitrary numbers of domains.
See also smash sum , disjoint union .
2. A Unix utility to calculate a 16-bit checksum of the data in a file. It also displays the size of the file, either in kilobyte s or in 512-byte blocks. The checksum may differ on machines with 16-bit and 32-bit ints.
Unix manual page : sum(1).
(1995-03-16)