Two functions are "almost" equal, they differ only in x=1
The function f_1(x) = (x-1)/(x^2-x) has a point P, while f_2(x)=1/x, the point Q. The two points overlap when parameter t is animated, except for t=1, where P disappears for a second, the property is used for example to compute the limit of the function f_1 for x=1.