It is really a good paper that reviews the principle research fields in complexity theory with clear structure and simplified explanation, uncovering the nature of complexity. Generally, complexity theory describes objects with nonlinear relationships between changing entities with qualitative characteristics examined and how interactions change over time, etc. And the author breaks the complexity theory into three major parts: algorithm complexity, deterministic complexity and aggerate complexity. However, I am still a little confused about why it should be divided into those three parts? Is that possible if we think about and explain well complexity theory in time complexity and spatial complexity?

Should most of research question have to take into account the complexity theory because most of objects in natural environment and human society do have the general characteristics that complexity theory deals with? And it is really interesting when talking about self-organized system that will receive balance between randomness and stasis like peatlands ecosystem. But how complexity theory that helps explore the self-organization in physical geosicence be applied in social economical study is really appealing. There is still some unclear space in complexity theory study. How could new developing techniques like GeoAI and spatial data mining that extract more hidden knowledge help complexity step further? These are all interesting and exciting questions to be answered in the future.