Non-idempotency conjecture for connected choice in dimension two

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Let \rm\sffamily CC2_2 denote connected choice for non-empty connected closed subsets of [0,1]2[0,1]^2. For a multi-valued operation ff, write f×ff\times f for two parallel instances of ff; an operation is idempotent when f×f≡Wff\times f\equiv_{\mathrm{W}}f. Idempotency conjecture. Connected choice in dimension two is not idempotent:

\sffamilyCC2×\sffamilyCC2̸≡W\sffamilyCC2.\text{\rm\sffamily CC}_2\times\text{\rm\sffamily CC}_2\not\equiv_{\mathrm{W}}\text{\rm\sffamily CC}_2.

The paper proves that connected choice in dimension one is not idempotent and explains that the conjecture would strengthen the corresponding Brouwer fixed point conjecture. The dimension-two case remains open.

References

Primary source

Vasco Brattka, Stéphane Le Roux, Joseph S. Miller and Arno Pauly, “Connected Choice and the Brouwer Fixed Point Theorem”, arXiv:1206.4809 (2018).

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