PACS:61.30.Jf, 61.30.Eb, 61.30.Gd, 64.70.Md (all) DOI:10.1070/PU1988v031n03ABEH005710 URL: https://ufn.ru/en/articles/1988/3/b/ Citation: Kurik M V, Lavrentovich O D "Defects in liquid crystals: homotopy theory and experimental studies" Sov. Phys. Usp.31 196–224 (1988)