least fixed point definition mathematics
f may have many fixed points (x such that f x = x). For example, any value is a fixed point of the identity function, (\ x . x).
If f is recursive
, we can represent it as
f = fix F
where F is some higher-order function
fix F = F (fix F).
The standard denotational semantics
of f is then given by the least fixed point of F. This is the least upper bound
of the infinite sequence (the ascending Kleene chain) obtained by repeatedly applying F to the totally undefined value, bottom. I.e.
fix F = LUB bottom, F bottom, F (F bottom), ....
The least fixed point is guaranteed to exist for a continuous
function over a cpo