theory In domain theory, a
function, f, which is (a)
idempotent, i.e. f(f(x))=f(x) and (b) whose result is no
more defined than its argument. E.g. F(x)=bottom or F(x)=x.
In
reduction systems, a function which returns some
component of its argument. E.g. head, tail, (x,y) . x.
pointer to part of its argument and does not need to build any
new graph.
(1997-01-29)