Let f: X → X be a function. A point x for which f(x) = x> is called a *fixpoint* of f.

If f is continuous, and if the sequence a, f(a), f(f(a)), f(f(f(a))), ... converges to some limit b, then b is a fixpoint of f. Unfortunately, the converse is not true: not every fixpoint is such a limit (only an attracting fixpoint). Additionally, the sequence a, f(a), f(f(a)), ... need not *have* a limit. For instance, if f is "rotate 32°" on **R**^{2}, then for any a≠0 the sequence has no limit; despite this, a=0 is a fixpoint of f.