Douglas Hofstadter coined this term: where an upwards (or downwards) traversal of the levels in a hierarchical system takes one back to one’s starting point.
To loop is to return without reversal.
Strange Loop
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GEB Introduction
The last canon he describes is an endlessly rising canon, where 3 voices create a cycle that sounds as though it rises without end. It’s not simply a spiral, but maybe like a toroidal spiral? In taiji, it’s like the path power takes in the Positive and Negative Circles. He calls this a Strange Loop: where an upwards traversal of the levels in a hierarchical system takes one back to one’s starting point.