A semiring S with two additional properties:
A special unary operation called
closure can be defined on closed semirings. Given an element
a in
S, powers can be defined in the expected manner:
Then the closure
a* can be defined as follows:
The properties of a semiring imply that
Closed semirings have applications in various branches of computing such as automata theory, the theory of grammars, the theory of recursion and fixed points, sequential machines, aspects of matrix manipulation, and various problems involving graphs, e.g. finding shortest-path algorithms within graphs.