K jedné matematické úloze o vlasech
A function f: ℝⁿ → ℝ satisfies the condition (resp. , ) at a point x if for each real r > 0 and for each set U ∋ x open in the Euclidean topology of ℝⁿ (resp. strong density topology, ordinary density topology) there is an open set I such that I ∩ U ≠ ∅ and . Kempisty’s theorem concerning the product quasicontinuity is investigated for the above notions.