Strange Loop

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A strange loop arises when, by moving only upwards or downwards through a hierarchical system, one finds oneself back where one started. Strange loops may involve self-reference and paradox. The concept of a strange loop was proposed and extensively discussed by Douglas Hofstadter in Gödel, Escher, Bach, and is further elaborated in Hofstadter's book I Am a Strange Loop, published in 2007. A tangled hierarchy is a hierarchical system in which a strange loop appears.