When do we have a minimum phase

I am a DSP newbie and I am really confused after reading Chapter two of

"An Introduction to Digital Signal Processing by J. H. Karl".

On page 32, first paragraph, the book defines a minimum phase couplet as one with zeros OUTSIDE the unit circle of the z-plane. But I have read everywhere else that a minimum phase system has all zeros and poles INSIDE the unit circle.

Is this a contradiction? When do we have a minimum phase couplet?

Answer 1

[Li Kang]

1. The minimum phase system can promise that both zeros and poles are IN the unit cycle.

2. If the system has minimum phase, it is easy to counteract its effects by merely alternating the numerator and denominator. Since both zeros and poles are IN the unit cycle, the stability is ensured after the alternation.