The converse chordality conjecture for positive definite function extensions
Let be a group, let , and let be the associated graph. A function is positive definite if its corresponding kernels satisfy the positive-definiteness condition used for operator-valued functions.
Converse chordality conjecture. For every such that is not chordal, there exists a positive definite function
which does admit a positive definite extension to .
This conjecture proposes the reciprocal of the paper's extension theorem: nonchordality should guarantee the existence of a positive definite function on that extends positively to the whole group. The supplied text gives no evidence that the conjecture has been resolved.
References
Primary source
M. Bakonyi and D. Timotin, “Extensions of positive definite functions on amenable groups”, arXiv:0808.1273 (2008).
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