[1] P. VOPĚNKA: The limits of sheaves and applications on constructions of models. Bull. Acad. Polon. Sci., sér. mat., astr. et phys., XIII (1965), 189-192. MR 0182570

[2] P. VOPĚNKA: On $\nabla $-model of set theory. ibid., 267-272. MR 0182571

[3] P. VOPĚNKA: Properties of $\nabla $ -model. ibid., 441-444. MR 0189984

[4] P. VOPĚNKA: $\nabla $ -models in which the generalized continuum hypothesis does not hold. ibid., XIV (1966), 95-99. MR 0200142

[5] P. VOPĚNKA, P. HÁJEK: Permutation submodels of the model $\nabla $. ibid., XIII (1965), 611-614. MR 0194320

[6] P. HÁJEK, P. VOPĚNKA: Some permutation submodels of the model $\nabla $. ibid., XIV (1966), 1-7. MR 0194321

[7] P. VOPĚNKA: Limits of sheaves over compact Hausdorff extremally disconnected spaces. ibid. (in press).

[8] P. VOPĚNKA, P. HÁJEK: Concerning the $\nabla $ -models of set theory. ibid. (in press).

[9] P. VOPĚNKA: Modeli teorii množestv. (in Russian), Zeitschrift f. Math. Logik und Grundlagen der Math. 8 (1962), 281-292. MR 0146085

[10] P. HÁJEK: Die durch die schwach inneren Relationen gegebenen Modelle der Mengenlehre. ibid., 10 (1964), 151-157. MR 0164888