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).

(1995-03-16)