A fixed point is indifferent if
some nearby points iterate toward the fixed point and other nearby points iterate
away from the fixed point, or if they do not move at all. 

Click the animation to stop. 
If a fixed point is indifferent, at the fixed point the tangent
line to the graph has slope +1. 
However, merely having slope +1 does not guarantee
a fixed point is indifferent. 
Some stable fixed points have tangents with slope +1;
some unstable fixed points have tangents with slope +1. Which behavior occurs can be
determined by graphical iteration. 