Sorry, did not make the notion of deformation precise. The idea is that stretching and compressing cannot include attaching one part to another, or tearing it. The mathematical term is that of a "homeomorphism" , which is a one to one, onto, and continuous map. The precise statement is that the figure 8 is not homeomorphic to zero. A good place to look is
Yeah, I've met the concept during my studies and was rather teasing for getting a great popular, easy to grasp, explanation which would also fit the definition.
It's not easy to find a fitting visual analogy TBH, which I'd find generally useful as I hold the concept to enhance general thinking.
Sorry, did not make the notion of deformation precise. The idea is that stretching and compressing cannot include attaching one part to another, or tearing it. The mathematical term is that of a "homeomorphism" , which is a one to one, onto, and continuous map. The precise statement is that the figure 8 is not homeomorphic to zero. A good place to look is
https://www.google.com/books/edition/Basic_Topology/NJbuBwAAQBAJ?hl=en&gbpv=1&printsec=frontcover