TY JOUR TI New Problems of Descriptive Geometry KW analytical figure KW synthetic figure KW imaginary sphere KW imaginary cylinder KW degenerated surfaces KW null sphere KW null cylinder KW imaginary complement KW isotropes KW contact KW intersection KW 4D figures JO Geometry & Graphics AU Girsh, A.G. PY 2019 IS 7 PB INFRA-M Academic Publishing LLC.