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2. The direct lags.

2.1 The first order lag - low-pass filter. 

2.2 The first order lag - high-pass filter.

2.3 The second order lag - roots are real.

2.4 The second order lag - roots are complex.

2.5 The second order lag - roots are equal.

2.6 The second order lag - real equals imaginary.

2.7 The second order lag - band-pass (roots are real).

2.8 The second order lag - band-stop (roots are complex).

3. The inverse lags (controllers).

3.1 The inverse first order lag (inverse low pass filter) - PD-controller.

3.2 The inverse first order lag (inverse high-pass filter) - PI-controller.

3.3 The inverse second order lag (inverse bandpass) - PID-controller.