In post 57 and in 59 too Vp is a voltage at OpAmp non-inverting input.

 

"But for Vin > -4V the voltage at output would have been negative (Vin = -4.01V --->Vn = 4V - 4.01V = -0.01V)"
Just to clarify, when Vin approaches -4.01V, Vn(inverting) equals to 4V(across the capacitor) -4.01V(Vin)=-0.01V
Am I correct?

 

Yes you are correct.

 

Dear Jony130
ok learned it thankkkksss