x_{1} is a generalized cylinder (see notes for details) of form/shape x_{2}.

x_{1} is a set of points/shape (of any number of dimensions) such that x_{1} is connected and there exists a line L such that for any line L' that is parallel to L, if L' has nonempty intersection with x_{1}, then there exists exactly one subinterval (line segment, ray, or line) J of L' such that J has nonzero (Lebesgue) measure and any subset of L' which nonemptily intersects x_{1} is contained in J. An axially-perpendicular cross-section of x_{1} probably is necessary to specify x_{2}. See also: slanu, fru'austumu.