Grätzer, George; Wenzel, G. H. (1990). "Notes on tolerance relations of lattices". Acta Scientiarum Mathematicarum. 54 (3–4): 229–240. ISSN0001-6969. MR1096802. Zbl0727.06011.
Poincare, H. (1905). Science and Hypothesis (with a preface by J.Larmor ed.). New York: 3 East 14th Street: The Walter Scott Publishing Co., Ltd. pp. 22-23.{{cite book}}: CS1 maint: location (link)
Grätzer, George; Wenzel, G. H. (1990). "Notes on tolerance relations of lattices". Acta Scientiarum Mathematicarum. 54 (3–4): 229–240. ISSN0001-6969. MR1096802. Zbl0727.06011.
Grätzer, George; Wenzel, G. H. (1990). "Notes on tolerance relations of lattices". Acta Scientiarum Mathematicarum. 54 (3–4): 229–240. ISSN0001-6969. MR1096802. Zbl0727.06011.