@article{201811.0301,
	doi = {},
	url = {https://doi.org/},
	year = 2020,
	month = {February},
	publisher = {Preprints},
	author = {Apoloniusz Tyszka},
	title = {Open Problems on Computable Sets {${\mathcal X} \subseteq N$}, Which Require That a Known Integer $n$ Satisfies ${\rm card}({\mathcal X})=\omega \Leftrightarrow {\mathcal X} \cap (n,\infty) \neq \emptyset$, and Which Cannot Be Stated Formally as They Refer to Current Knowledge about ${\mathcal X}$}},
	journal = {Preprints}
}