A function has a spinode (also called a horizontal cusp) at a point if is continuous at and

from one side while

from the other side, so the curve is continuous but the derivative is not.s

A function has a spinode (also called a horizontal cusp) at a point if is continuous at and

from one side while

from the other side, so the curve is continuous but the derivative is not.s

Weisstein, Eric W. "Spinode." From *MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/Spinode.html