# About why Danielewski surfaces are the counterexamples for cancellation problem

The Danielewski surfaces $xy^n=1-z^2$ are the famous counterexamples for cancellation problem for affine spaces. I'm asking where to find the articles telling the whole story. Especially how to distinguish them in the sense of isomorphism(I heard it involves the fundamental group at infinity, which I'm quite curious about but not familiar with). I tried google scholar but the papers are investigating other properties of them.

Thanks!

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