Let
be a one-parameter family of
map satisfying
then there exist intervals ,
and
such that
1. If ,
then
has two fixed points in
with the positive one being unstable and
the negative one stable, and
2. If ,
then
has no fixed points in
.
This type of bifurcation is known as a fold bifurcation, sometimes also called a saddle-node bifurcation or tangent bifurcation. An example of an equation displaying a fold bifurcation is
(Guckenheimer and Holmes 1997, p. 145).