In the technical literature you find the following description: "A Schmitt trigger circuit is a comparator circuit comprising a positive feedback, so that the switch-on and switch-off threshold do not coincide."
In a positive feedback (also called regenerative feedback) the output of the comparator is connected with the input. For this you use the resistor R3.
Turning the potentiometer P1 you quickly realize that the switch-on and switch-off points no longer coincide! You have added a hysteresis to the voltage comparator.
You have again the typical behavior of all Schmitt triggers.
However, you want to have a closer look...