The question, written so it cannot collapse

The question is therefore

Three statements that are not this question: $u\notin {\mathcal{F}}_{\mathrm{mc},\mathrm{pol}}$, already XI-F's Theorem F1; the one-slot rewriting of a boundary trace, true for one slot and not a theorem for two; and the existence of some larger bimodule containing a singular kernel, which XI-E's correction leaves open and which this paper does not touch.