Because there is no DC negative feedback, the circuit cannot work in the linear region. So this circuit is a pulse shaping circuit, which shapes the input wave signal into a square wave signal (the output is only in high and low voltage state).
The circuits of R 1 and C 1 are acceleration circuits, aiming at increasing the steepness of the pulse front.
R2 controls the threshold voltage inverted by the circuit.
Because it is a positive feedback loop, C3 and C2 must be added to make the AC amplification zero and prevent high-frequency self-excited oscillation.