Sum
1. <theory> In
domain theory, the sum A + B of two
domains 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 isA(x) -> E1; isB(x) -> E2
This can be generalised to arbitrary numbers of domains.
See also
smash sum,
disjoint union.
2. <tool> 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
kilobytes or in 512-byte blocks.
The checksum may differ on machines with 16-bit and 32-bit ints.
Unix manual page: sum(1).
