projection
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.
In a {graph reduction} system the function can just return a
pointer to part of its argument and does not need to build any
new graph.
(1997-01-29)