[3] J. Niederle: On skeletal and irreducible elements in tolerance lattices of finite distributive lattices. Časop. pěst. matem. 107 (1982), 23 - 29. DOI 10.21136/CPM.1982.108319 | MR 0651079 | Zbl 0484.06015
[4] J. Niederle: Tolerances on frames. Arch. Math. (Brno) [Submitted.] MR 1189644